I'm getting all sorts of rendering engine errors in IE7 here, when you set a DOCTYPE it should be accurate for your markup, currently you have this:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
However your page is not at all XHTML Strict compliant, and not really XHTML Transitional compliant either. You should pick the DOCTYPE you're after then fix the validation errors that remain, I'm not saying it has to be 100% valid to render, I'm just saying that's the wall I currently hit viewing your page, there may be another once you fix this...but that is unlikely since it works in other browsers.
Invalid HTML will give you all sorts of weird behavior, it's best to fix them if for no other reason than ruling out the invalid HTML as the cause. A browser maker is free to assume the HTML is valid, and do things based on that (using the same ID multiple times is the most common example, it's a hash table in most browsers)...if it's not valid and that screws something up, well the browser is also free to not care :)