Here are a few things you can try:
-- If it's not related to having changed any options or installing ad blocking programs (which can also block some graphics and animations) then you may need to repair your browser. The last few versions of Internet Explorer have a repair feature. Go to Control Panel, Add/Remove Programs, highlight Microsoft Internet Explorer in the list of programs, click Add/Remove, a box will come up that gives you various options, select Repair. This will repair damaged files and return IE to it's default settings.
-- Something else that might help out is to delete your internet cache. More specifically, click on the tools menu, go down to Internet Options, then click on Delete files. IE may have problems displaying some images when it has alot of pages stored, and is sometimes not able to automatically delete the old stuff to make room for the new.
-- If those two don't work, then see if you fit into previously reported display problems. Here are some that may fit. You can also do a search. If none of these fit either, then I recommend you submit a report to microsoft and see what they think the problem is causing it.
for older IE browsers:
I'm sure it is very frustraiting for you, but it's frustrating for us also who can't reproduce this. BTW, nice flash graphic on your site.