USB Wireless adapter says there is internet connection, but cannot access internet?

[Vegas Matt]

A friend of mine has a Netgear USB wireless adapter on their desktop (running Windows XP). The Netgear software says there is a connection to the internet (via her wireless router), and the icon in the bottom right of the screen says there is an internet connection, but when she tries to run Explorer or anything else using the internet, it says there is no connection.

Anyone know what the problem could be? Is there a good website that could help me with this problem?
"Turn off DHCP, type your DNS server addresses in manually, try again. "

I have no idea what this means.
Also, the modem works fine. There is another computer connected (not wirelessly) and it works fine.