Beside XP, did you install drivers for motherboard, video, audio, LAN and what else?
I recently reformated my XP machine, and re-installed windows xp. Since then i have not been able to connect to the internet through my router, there are several other machines on the network which dont have a problem connecting. It seems to be nothing to do with the router as i plugged my cable into the back of another pc and the internet ran fine. My TCP/IP settings are such that it obtains an IP adress automatically, but the IP adress it is getting i think is wrong. the other pc's get IP addresses starting 192.168.xx.xx, however mine gets something completely different, in device manager my network card says it is working fine.