Jquery AJAX Form Submission/Coldfusion

I really like the 2nd option...but what do you mean by have the server return a http error on a duplicate email?  

Currently I am trying to use a simple query to tell if the email address exists:
<cfquery name="check" datasource="lbdb_">
Select * from tbl_member
where member_email = '#url.email#'
</cfquery>

<cfif check.recordCount eq 0>
    query to insert into database and a message to the user
</cfif>

What would I have to do to get your 2nd option to work?  

Thanks for the help.  

Sorry for the delayed response...my day got cut short yesterday.  

I tried using cfheader and it shows the error when I use firebug, but it doesn't actually fire off the error function I defined.  I've attached a snippet of the code, maybe I'm doing something wrong.

Here is main part of my js file

$.ajax({
      type: "POST",
      url: "addMember.cfm?" + dataString,
      data: dataString,
      success: function(result) {
        $('#contact_form').html(result);
      }
	  error: function() {
		alert('hello'); 
	  }
     });

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Here is my coldfusion file

<cfset cDate = dateformat(now(), 'mm/dd/yyyy')>
<cfquery name="check" datasource="lbdb_">
Select * from tbl_member
where member_email = '#url.email#'
</cfquery>

<cfif check.recordCount eq 0>
    <cfquery name="addMember" datasource="lbdb_">
        insert into tbl_member (member_name, member_email, member_date)
        values ('#url.name#', '#url.email#', #createODBCDate(cdate)#)
    </cfquery>
    <div id="message">Thank you for subscribing</div>
<cfelse>
    <cfheader statuscode="400" statustext="Bad Request" />
    <cfabort />
</cfif>

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Thanks for the help.  I got it to work!