I have a similar problem. VISTA64 Bit Home premium, IE8,Firefox 3 and Safari Beta 4 as the browsers,AVAST home 4.8
From time to time on clicking on a link the browser just seems to hang. The small VISTA circle just keeps doing its thing and the page never loads. So Shut down the browser and re start it. Now I am locked the Browser just sits there trying to connect to my homepage.
This occurs with all 3 Browsers.
The solution is to Exit the browser, turn of AVAST ON Access protection. Re start the browser which then works quite happily. I then shut down the browser and re activate AVAST On access protection and re start the browser. things are back to normal until the next time it happens. Its random but I get about 3 times a day.