To check if it's spybot, hit the IE tools menu /spybot entry. When my browser craps out, I run x-setup's clean up code pages plugin. Try doing a thorough virus/trojan/worm/general slimy thing scan. Check the HOSTS file. In IE, check the Restricted sites. Search the registry for any reference to a site that doesn't work.

I'm running Vista 32-bit, with both Office 2007 and IE 8 beta, and haven't run into this problem. I also use Avast (paid version), ccleaner, jkdefrag. Check Windows Defender and Firewall settings. And there's an MSKB article on nLite.

In other words, throw everything at the wall and see what sticks.