Do you get a message saying "limited or no connectivity" ? I'm not sure why they say "limited" - it really means no connectivity at all. It usually happens when the wireless card doesn't get an IP address from the router. So Windows just makes up one of its own!
Try setting the IP address, Subnet mask, Gateway and DNS settings of your card manually. Let me know if you need some instructions on how to do this and I'll write some up for you