Hi Michele,
I see this problem on your site when I view it in IE 8 mode but I can't seem to reproduce the problem on my local machine using .NET 4.5.
I "think" if you change the HTML question(s) on your form to plain paragraph questions it will solve the problem.
The HTML question type uses the html wysiwyg editor from the ajaxcontroltoolkit and it may have some problems in IE 8, or maybe only the .NET 3.5 version of the editor has this problem since I can't reproduce it on .NET 4.5. The popup window is definitely coming from the ajaxtoolkit wysiwyg editor so by removing html question types it should remove that form the page.
Hope that helps,
Joe