Try to turn off any firewall you have running on that computer.
Then check that the wireless adapter is installed and functioning properly in Device Manager.
Then check that the DHCP client is started in start>run>services.msc
Run winsock xp
WinSock XP Fix download and review - fix XP internet connectivity from SnapFiles
Remove your wireless setting and redo it again (enter SSID, encryption, etc) in the properties of the wireless card/wireless tab if you use Windows wireless management.