addresses for both PCs, as well as the default gateway. Found in Network Properties, they should all be in the same range.
Next I would check if the non-Internet machine can connect if the other is off.
Fianlly ICS (Internet Connection Sharing) should not be used while a router is dishing out the IPs.
I have 2 computers, both using Windows XP. Both are connected to a Linksys wireless G router, but only 1 gets internet access. The internet light and the lights on both ports where the ethernet cables are connected are flashing. I have tried switching ethernet cables, but I still don't have a connection on both computers. What should I do?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic