Swapping the motherboard and various other fundamental parts and expecting the OS to carry on working is just not realistic I'm afraid.
It's more than likely that both OSes are missing modules or drivers required to address your new hardware.
Try booting a Linux Live CD (I recommend
Ubuntu) and see if it works. If it does then there's nothing wrong with your equipment and you just need to reinstall the OS. With Windows, you might get away with a repair install which keeps the registry and installed programs/users/settings in tact - boot off the XP CD, go to install (do
NOT press R to repair, that drops you to the recovery console) select the partition, at some point it will prompt you to overwrite or repair.