How do I integrate an external form which is a pop up / dynamic form?

Hi

I have to integrate external forms from a webpage into ELOQUA to collect the form submissions...

The form in question though is a kind of pop up form on a main page -- so it's on a webpage with a URL -- BUT isn't ON the page so to speak ...

How do I integrate it in ELOQUA and enable it so I can collate the forms submits?

Thanks!