Can't connect to the internet.?

So I am visiting my kids. They have two computers both on the same network. The downstairs runs Vista, and was full of viruses. I ran AVG and found a bunch of stuff. When it cleaned it off, the Vista system cannot connect to the internet. This one still can as you see, and is running XP. I reinstalled firefox hoping that might do it, but nope. Firefox, iTunes, IE, Flock. Nothing gets out and I get page not found sort of errors.

So, I can get to the net, but not on the newly virus free system.

Any ideas other than re-install the O/S?

Thanks,

Mike -