form validation script....

I need to validate this form...but before its submitted it needs to check in the SQL Server DB that the username they want is not already taken, then it needs to check they have entered their email twice, and that they match, and the same for password, it also needs to validate the email for a @ and . and needs to make sure all fields have something entered (apart from non-required ones) as well as make sure the right amount of characters have been entered. After the form I have put the functions I already have. Thanks:

<div class="registrationForm" name="registrationForm">

<form name="REGISTRATION" method="POST" action="#" ID="Form1">

<div class="accountType">
<table width="452" border="0" cellpadding="2" cellspacing="0" class="registrationForm" ID="Table2">
  <tr>
    <td colspan="3" class="critical"><b>All fields in RED are required</b></td>
  </tr>  
  <tr>
    <td colspan="3" class="sectionName">Choose Account</td>
  </tr>
  <tr>
    <td colspan="3"><hr class="registrationForm"></td>
  </tr>  
  <tr>
    <td class="critical">Account Type</td>
    <td class="field">
            <b>FREE ACCESS UNTIL - (date here)</b>
    </td>
    <td><a href="#" class="help" onmouseover="showtip(this,event,'CHOOSE YOUR TYPE OF ACCOUNT. TRIALS ARE FOR A PERIOD OF FIVE DAYS')" onmouseout="hidetip()">?</a></td>    
  </tr>
</table>

</div>
<br>
<div class="address">
<table width="452" border="0" cellpadding="2" cellspacing="0" class="registrationForm" ID="Table1">
  <tr>
    <td colspan="3" class="sectionName">Personal Details and Address</td>
  </tr>
  <tr>
    <td colspan="3"><hr class="registrationForm"></td>
  </tr>  
  <tr>
    <td class="critical">Preferred User Name</td>
    <td class="field"><input type="text" class="registrationFormADDRESS" name="userName" ID="Text1">
    </td>
    <td><a href="#" class="help" onmouseover="showtip(this,event,'USED TO LOG INTO FFS')" onmouseout="hidetip()">?</a></td>    
  </tr>
  <tr>
    <td class="critical"></td>
    <td class="characterCount">
    <script>
      displaylimit("document.REGISTRATION.userName",20)
      </script>
    </td>
    <td></td>    
  </tr>
  <tr>
    <td class="critical">Your Email Address</td>
    <td class="field"><input type="text" class="registrationFormADDRESS" name="userEmailOne" ID="Text2"></td>
      <td><a href="#" class="help" onmouseover="showtip(this,event,'MUST BE VALID TO ACTIVATE YOUR ACCOUNT AND MATCH THE CONFIRMING EMAIL')" onmouseout="hidetip()">?</a></td>  
  </tr>
  <tr>
    <td class="critical">Confirm Email</td>
    <td class="field"><input type="text" class="registrationFormADDRESS" name="userEmailTwo" ID="Text3"></td>
      <td><a href="#" class="help" onmouseover="showtip(this,event,'MUST MATCH YOUR EMAIL ADDRESS')" onmouseout="hidetip()">?</a></td>      
  </tr>  
  <tr>
    <td class="critical">Password</td>
    <td class="field"><input type="password" class="registrationFormADDRESS" name="" ID="Password1"></td>
      <td><a href="#" class="help" onmouseover="showtip(this,event,'CHOOSE A PASSWORD. THIS IS NOT CASE SENSITIVE. MUST BE CONFIRMED BELOW')" onmouseout="hidetip()">?</a></td>      
  </tr>
  <tr>
    <td class="critical">Confirm Password</td>
    <td class="field"><input type="password" class="registrationFormADDRESS" name="" ID="Text4"></td>
      <td><a href="#" class="help" onmouseover="showtip(this,event,'CONFIRM YOUR PASSWORD')" onmouseout="hidetip()">?</a></td>      
  </tr>
  <tr>
    <td class="field">Street Address</td>
    <td class="field"><input type="text" class="registrationFormADDRESS" name="" ID="Text5"></td>
      <td><a href="#" class="help" onmouseover="showtip(this,event,'HOUSE NUMBER AND STREET')" onmouseout="hidetip()">?</a></td>      
  </tr>
  <tr>
    <td>Village</td>
    <td class="field"><input type="text" class="registrationFormADDRESS" name="" ID="Text6"></td>
      <td><a href="#" class="help" onmouseover="showtip(this,event,'YOUR VILLAGE, IF APPLICABLE')" onmouseout="hidetip()">?</a></td>      
  </tr>
  <tr>
    <td>Town</td>
    <td class="field"><input type="text" class="registrationFormADDRESS" name="" ID="Text7"></td>
      <td><a href="#" class="help" onmouseover="showtip(this,event,'YOUR TOWN, IF APPLICABLE')" onmouseout="hidetip()">?</a></td>      
  </tr>
  <tr>
    <td class="critical">City</td>
    <td class="field"><input type="text" class="registrationFormADDRESS" name="" ID="Text8"></td>
      <td><a href="#" class="help" onmouseover="showtip(this,event,'YOUR CITY')" onmouseout="hidetip()">?</a></td>      
  </tr>
  <tr>
    <td class="field">County</td>
    <td class="field"><input type="text" class="registrationFormADDRESS" name="" ID="Text9"></td>
      <td><a href="#" class="help" onmouseover="showtip(this,event,'YOUR COUNTY')" onmouseout="hidetip()">?</a></td>      
  </tr>
  <tr>
    <td class="field">Postcode</td>
    <td class="field"><input type="text" class="registrationFormADDRESS" name="postCode" ID="Text10"></td>
      <td><a href="#" class="help" onmouseover="showtip(this,event,'YOUR POSTCODE')" onmouseout="hidetip()">?</a></td>      
  </tr>
  <tr>
    <td class="critical">Country</td>
    <td class="field"><input type="text" class="registrationFormADDRESS" name="" ID="Text11"></td>
      <td><a href="#" class="help" onmouseover="showtip(this,event,'YOUR COUNTRY')" onmouseout="hidetip()">?</a></td>      
  </tr>
  <tr>
    <td>Home Telephone</td>
    <td class="field"><input type="text" class="registrationFormADDRESS" name="homePhone" ID="Text12"></td>
      <td><a href="#" class="help" onmouseover="showtip(this,event,'HOME TELEPHONE NUMBER')" onmouseout="hidetip()">?</a></td>      
  </tr>  
  <tr>
    <td>Mobile Telephone</td>
    <td class="field"><input type="text" class="registrationFormADDRESS" name="mobilePhone" ID="Text13"></td>
      <td><a href="#" class="help" onmouseover="showtip(this,event,'WE AIM TO LAUNCH A MEMBERS SMS SERVICE IN THE SECOND QUARTER OF 2003. YOUR MOBILE NUMBER WILL BE REQUIRED TO USE THIS')" onmouseout="hidetip()">?</a></td>      
  </tr>
  <tr>
    <td colspan="2" width="400"><b>You must accept the terms and conditions</b><input type="checkbox" name="TOS" ID="Checkbox1"></td>
      <td><a href="#" class="help" onmouseover="showtip(this,event,'YOU MUST ACCEPT THE TERMS AND CONDITIONS OF SERVICE IN ORDER TO SUBMIT THIS FORM')" onmouseout="hidetip()">?</a></td>      
  </tr>
  <tr>
    <td colspan="2" width="400"><INPUT type="submit" value="Submit" ID="Submit1" NAME="Submit1" onClick="checkEmail();"></td>
      <td><a href="#" class="help"></a></td>      
  </tr>  
</form>
 
</table>

</div>

SCRIPT FOR PAYMENT DETAILS:

var isIE=document.all?true:false;
var isDOM=document.getElementById?true:false;
var isNS4=document.layers?true:false;

/* _w : which ID (1) or (2) */
/* _h : (h)ide or (s)how */
function toggleT(_w,_h) {
  if (isDOM)
  {
    if (_h=='s') document.getElementById(_w).style.visibility='visible';
    if (_h=='h') document.getElementById(_w).style.visibility='hidden';
  }
  else if (isIE) {
    if (_h=='s') eval("document.all."+_w+".style.visibility='visible';");
    if (_h=='h') eval("document.all."+_w+".style.display='inline';");
  }
  else if(isNS4)
  {
    if (_h=='s') eval("document.layers['"+_w+"'].visibility='show';");
    if (_h=='h') eval("document.layers['"+_w+"'].visibility='hide';");
  }
}

SCRIPT TO COUNT REMAINING CHARACTERS:

var ns6=document.getElementById&&!document.all

function restrictinput(maxlength,e,placeholder){
if (window.event&&event.srcElement.value.length>=maxlength)
return false
else if (e.target&&e.target==eval(placeholder)&&e.target.value.length>=maxlength){
var pressedkey=/[a-zA-Z0-9\.\,\/]/ //detect alphanumeric keys
if (pressedkey.test(String.fromCharCode(e.which)))
e.stopPropagation()
}
}

function countlimit(maxlength,e,placeholder){
var theform=eval(placeholder)
var lengthleft=maxlength-theform.value.length
var placeholderobj=document.all? document.all[placeholder] : document.getElementById(placeholder)
if (window.event||e.target&&e.target==eval(placeholder)){
if (lengthleft<0)
theform.value=theform.value.substring(0,maxlength)
placeholderobj.innerHTML=lengthleft
}
}


function displaylimit(theform,thelimit){
var limit_text='<b><span id="'+theform.toString()+'">'+thelimit+'</span></b> characters remaining'
if (document.all||ns6)
document.write(limit_text)
if (document.all){
eval(theform).onkeypress=function(){ return restrictinput(thelimit,event,theform)}
eval(theform).onkeyup=function(){ countlimit(thelimit,event,theform)}
}
else if (ns6){
document.body.addEventListener('keypress', function(event) { restrictinput(thelimit,event,theform) }, true);
document.body.addEventListener('keyup', function(event) { countlimit(thelimit,event,theform) }, true);
}
}

SCRIPT TO HIGHLIGHT FIELDS:

var focusColor = '#E1E1E1';
var blurColor = '#ffffff';

function hotbox() {
var form, el, e, f = 0;
while (form = document.forms[f++]) {
e = 0;

while (el = form.elements[e++]) if (el.type == 'text' || el.type =='password' && typeof el.style != 'undefined') {
el.onfocus = new Function('this.style.background = "' + focusColor + '";' + 'this.style.border = "1px solid #B1B1B1";');
el.onblur = new Function('this.style.background = "' + blurColor + '";' + 'this.style.border = "1px solid #B1B1B1";');
}
}
}

onload = hotbox;

EMAIL CONFIRMATION SCRIPT:

function checkEmail(REGISTRATION) {
    if (document.REGISTRATION.userEmailOne.value != document.REGISTRATION.userEmailTwo.value)
    {
        alert('Those emails don\'t match!');
        return false;
    } else {
        return true;
    }
}

TOOLTIPS SCRIPTS:

function showtip(current,e,text)
{
   if (document.all)
   {
      thetitle=text.split('<br>')
      if (thetitle.length > 1)
      {
        thetitles=""
        for (i=0; i<thetitle.length; i++)
           thetitles += thetitle[i] + "\r\n"
        current.title = thetitles
      }
      else current.title = text
   }

   else if (document.layers)
   {
       document.tooltip.document.write(
           '<layer bgColor="#FFFFE7" style="border:1px ' +
           'solid black; font-size:12px;color:#000000;">' + text + '</layer>')
       document.tooltip.document.close()
       document.tooltip.left=e.pageX+5
       document.tooltip.top=e.pageY+5
       document.tooltip.visibility="show"
   }
}

function hidetip()
{
    if (document.layers)
        document.tooltip.visibility="hidden"
}

It may just be a question of combining the functions I already have?