It would help if you knew the chipset of the lan card..Vista might have told it, but I think you could use a live-cd Linux to try and determine it (lspci?)
Then when you know the chipset, you can try to search for a driver for that chipset for Linux or maybe even for XP..but it is completely possible that the driver for that chipset is released only for Vista and not XP (in Windows), so you might have trouble finding it for XP. These driver-things are a pain in the back sometimes..
If you can, post the relevant lspci-output here if somebody knew better then.