Adapter bad? Configuration? Driver?

A few days ago, one computer on my home network was
suddenly unable to access the internet using email, ssh,
or IE. I also can't access the rounter from that computer
although another computer plugged into the same router has
no problem accessing the internet as well as the router.

I have tried starting in safe mode with network support.
I've uninstalled and re-installed the network driver, run
the internet set-up wizard, and even tried reinstalling
Windows XP. Still, nothing.

Curiously, I can ping both the router and external
addresses (like yahoo). All packets are sent and received.

Any other things I might try? I'm wondering if there isn't
something wrong with the network adapter (which is
intergrated with my mobo -- is that possible?).

Thanks for your help!
-devin