Check both pc's have a spare pci slot. Buy a couple of NIC (network interface cards) and a length of crossover cable. Bung the cards in follow install instructions for drivers then set up network. Maplin do a Networking kit contaning all you need for about £15. or you can buy from Dabs or even PC World. This is assuming your two pc's are within reasonable distance and that a cable can be run from one to tother.
Good luck P