As someone else stated earlier (I have fixed something similar for a friend). Sometimes certain DSL access managers can cause this problem. In my friends case, he was using Bell's high speed Sympatico service and its access manager was at fault. He downloaded the latest access manager software which fixed it.
I've also ran into a similar problem with my Intel 10/100 card under XP but the card works fine in win2k and others. Anyway I dont this this is your problem. Access manager is probably at fault.
