DHTML Exit Popup

I need am exit DHTML popup that will show just before the visitor leaves my page. This popup needs to work on IE 7 (preferably 6 too), FireFox and Google Chrome. It must not have any javascript errors, and must be virtually unblockable.? If you can to a GetResponse (e-mail capture form) integration that would be awesome. Please let me know if you can do this and have experience with this.? Thanks for your bid.? ## Deliverables Additional info: the popup must be unblockable by all major browsers and I must be able to design it (change colors, background, add images etc)