JQuery include Form Parameter in output

Hello, I have a form that returns an error if the submit action fails.

The form is

<form action="" method="post" name="Register" class="fancyform" id="Register">
  <h3>Register</h3>
    <div class="notify">Please complete the form below and click 'Register'</div>
    <div class="alert" id="RegisterError" style="display:none;"></div><div class="halfbox">
    <label for="regfirstname">First name</label>
    <input name="regfirstname" type="text" required="required" id="regfirstname" form="Register" placeholder="First name" value="" maxlength="50" /><br/>
    </div>
    <div class="halfbox">
    <label for="regfirstname">Last name</label>
    <input name="reglastname" type="text" required="required" id="reglastname" form="Register" placeholder="Last name" maxlength="50" /><br/>
    </div>
    <div class="halfbox">
    <label for="regfirstname">Email</label>
    <input name="regemailaddress" type="email" required="required" id="regemailaddress" form="Register" placeholder="e.g joe.bloggs@yahoo.co.uk" pattern="[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,3}$" maxlength="135" /><br/>
    </div>
    <div class="halfbox">
    <label for="regfirstname">Password</label>
    <input name="regpassword" type="password" required="required" id="regpassword" form="Register" pattern="(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).{8,}" maxlength="50" /><br/>
    </div>
    <div class="labeldiv">
      <label title="Tick this option to have this computer / device store your login credentials">
                                                <input type="checkbox" name="rememberme" value="true" checked="checked">
                                                Remember me
      </label>
    </div>
    <input name="Register" type="submit" disabled="disabled" id="RegisterSubmit" form="Register" value="Register" />
  <input name="Cancel" type="button" class="cancelbutton closefb" id="RegisterCancel" onclick="$.fancybox.close()" value="Cancel" form="Register" />
  <input type="hidden" name="returnUrl3" value="">
</form>

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The JQuery is

  $("#Register").submit(function(e){
      e.preventDefault();
    $.ajax({
		type: "POST",
        url: "/actions/register.asp",
        data:$(this).serialize(),
		success:function(result){
          if(result==2){
            // do something success
     		 $.fancybox.close();
			 location.reload();
          }else {
            // do something fail
	      $('#RegisterError').html('<p>An account already exists with the username XXXXX. Please either <a class="fancybox" href="#SignIn" rel="nofollow">Login</a> or <a class="fancybox" href="#PasswordRequestfrm" rel="nofollow">Reset your password</a></p>');
          $('#RegisterError').fadeIn('slow');
          }
  	  }});
  });

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I want the section

$('#RegisterError').html('<p>An account already exists with the username XXXXX. Please

to replace the XXXXX with the form parameter value regemailaddress

Is this possible?

Thanks