I have this exact same problem.
I have two computers and one laptop connected to a host computer running DSL, and one computer and the laptop work fine on the internet and can load pages run MSN etc. But the last computer can only show that it's connected, otherwise, it can't load any webpages, or run any online programs.

I have manually set up the IP for this computer as it worked like this and never had any problems before this. If it makes any difference, the two clients that can connect to the host are macs. A desktop and a laptop, both connected fine.

If anyone knows how to fix this I would be greatly appreciated.