Normally I don't help ppl with pc's but I'm make this exception.
Do you have an option called "Internet Connection Sharing"? In XP, it's under Properties, Advanced settings from your connection in your "View Network Connections" folder. "Allow other network users to connect through this computer's internet connection" should have a checkmark. If not, turn it on. It might ask you which network to share with and select the one that uses your LAN. Viola!
