I'm making my site and I'm using Membership

I'm making my site and I'm using Membership and Marketpress. I made a custom form using Gravity Forms for the User Registration page on my site - It's a 5 page form with a progress bar . Used "as is," it works perfectly fine.

My dilemma is I would like to have it function as a pop-up, iframe maybe, or something similar. Basically, I don't want a full page to load for each of the 5 pages. I'd like to have a one fixed background and just the frame or "pop-up" box advance. I do have the pop-up plug in as well and I can't get a popup to work at all.

Any suggestions or advice or direction you can point me in. One more thing... I'm not a very advanced wordpress user but I' have gotten this far figuring most things out eventually.

I appreciate any help