My impression that this is an avast- related problem comes from the fact that while the pc worked perfectly before it was right after doing this last avast update that the internet connectivity was gone.
There is no other anti-virus programme installed on the vista partition at the moment - I did once try agp or whatever it was called with no success and removed it also. The avast installation has been working for some months with no problem - including a couple of programme- updates up until yesterday.