Other than CFForm

Suggestion:

1) let the cfform submit to the page in which the form is.

2) enclose the code that generates the modal window within a <cfif></cfif>

I shall illustrate with 2 CFM files:

testPage2.cfm

testPage2.cfm: Contents of the modal window. 

and

testPage1.cfm whose code is below

<cfif isDefined("form.fieldnames")>
<!--- Process the form here --->	
<cflog text="Welcome, #form.username#. This log confirms we're in the action page of the cfform in the modal window test" file="modalWindowTest" type="information">	

<!--- Modal window. Its content comes from testPage2.cfm --->
<cfwindow 
 name="ModalWindow" 
    title="Modal Window" 
    initshow="true" 
    resizable="false"
    height="400" 
    width="450"
    modal="true"
    source="testPage2.cfm">
</cfwindow>
</cfif>

<!--- Form submits to same page. That is, this same page is the form's action page.--->
<cfform action="#CGI.SCRIPT_NAME#">
<p>Please enter your name:
<cfinput type="Text" name="UserName" required="Yes"><p>
<input type="Submit" name="submit" value="Send"> 
<input type="RESET" name="reset" value="Reset">
</cfform>

Now check the log file, modalWindowTest.log

What have you tried?  What web development skills outside of ColdFusion do you have?  I don't consider this a ColdFusion-related issue unless you are specifically attempting to use the CFUI tags.

I use modal windows in my applications (both ColdFusion and non-ColdFusion) by using the jQuery Magnific Popup library.  Prior to using Magnific, we used the jquery ColorBox plugin.  Both of these plugins allow you to use a hidden div on your webpage without having to create an iFrame or perform an ajax request.  We use all 3 methods of generating forms based on what we are trying to accomplish.  Your needs may vary.

If you want to search for some alternatives, here's a Google search query for javascript modal libraries.

No help?
How to use modal windows with Coldfusion?
Thank you