Xbox 360 Live

[CherryCoke]

First of all if I put this in the wrong part of the forum please move it.
I'm new to the forum.

Alright I just recently got an Xbox 360 and a Linksys SEFBR41 4-port router, and am connecting my 360 and computer into my router, which is connected to my Speedstream 5100 modem via ethernet. My computer runs just perfect on the internet, no problems whatsoever. However when I attempt to run my 360 on Xbox Live, it tells me its wired, Ip address confirmed, but fails at DNS. My ISP is SBC Yahoo!. I tried just shutting everything off, unconnecting everything, waited about 10 - 20 minutes, and reconnected, still the problem consists. Please help.