I have the same problem, but my card is not an Nvidia, it's a realtek.
I can ping any ip address on the internet from the terminal, but just can't access web pages in firefox or emails in Thunderbird.

It's a dual boot with Windows Vista (which has no problem at all with web access).

I made my IP addresses static in OSOL disabling the automagic nwam crap.

Suggestions?

GMac