I did this for my previous company. Check out
www.evolveip.net and click on the Request Information button in the upper left. I used a WordPress plugin called "FancyBox" that I customized a little bit. It's basically an iFrame displaying within the shadowbox. If you wanted to delay an auto-popup either hit up a site like
www.dynamicdrive.com or write a JavaScript function to wait a few seconds after pageload then call your lightbox.
Hope this helps.