It could be a few things. The most obvious would be spyware. Get Spybot and HiJackThis to check your comp out. That should get rid of most of it.
The other is a bit harder. I have the problem too but on my Litestep side. I can't access any secure websites. I can't even download the hotfix from MS website because of the problem. It should say something like "script error" on the bottom left of the window. And based on a few websites, it's an activex script error.
Sorry if that's not much help...