I've seen this problem here at work on two PC's and OS's for over a year and only just figured out what was causing it a couple days ago. Basically, when I use IE with the Google toolbar activated I can only navigate to one or two pages before IE just sits there trying to connect. Once that happens I cannot connect to any more websites with that instance of IE and need to start another one.
However, when I switch off the Google toolbar or surf from within MS Outlook everything is fine.
Any ideas what might be causing this? Perhaps the firewall here at work?