Make sure your linksys device is acting as a DHCP server. Make sure your PC and your XBOX 360 are set to DHCP and are receiving it from the same scope (I.E. I have seen people have their DSL or CABLE modems also giving DHCP on different networks). Check your network settings from the PC with CMD from the run menu, IPCONFIG and it should show as an address given in the DHCP scope of your linksys. Since the linksys has a firewall, I recommend turning Windows Firewall off if you are running XP SP2.
The reason you are not seing a lot of people having this problem is because out of the box it should be working fine, it did for me and my friend that has one. The only reason it wouldn't work in my opinion, is if they were on different networks.
Edited by c-had, 27 February 2006 - 07:15 PM.