Nzealander and magmatrix,
Have you found a solution? I have the very same problem on a recent install of Vista Business.

The strange thing is that it affects only browsers, in my case both IE and Firefox. I can use Windows Live Messenger with no issues, even the advertising box on the bottom receives updates. I can also ping and resolve any domain but through the browsers I cannot reach any site until I reboot and then I might be good for an hour or so.

I don't think there is any problems with my rig. The only things on my system at the time the problem started were Firefox, avast antivirus, Spybot S&D, Windows Live Messenger and the Windows updates including SP1. And I don't have Internet Connection Sharing enabled so the fix from M$'s site wouldn't work for me. I have disabled the antivirus but that didn't work. Resetting the connection doesn't work.