If the computers don't have a network interface card you can go
buy a cheap null modem cable, and connect each end to the parallel or serial port on the back of the computers ( depending on what type of cable you bought, 25 pin one goes to the printer parallel port on each computer 9 pin connector goes to the smaller serial ports on each computer )
if you have windows 9x you can use a file transfer program in like start->programs->accessories I believe and it will use the null modem cable to transfer files between the computers
if you do decide to put network interface cards in , just get a crossover cable to connect the two together then you can setup a network and transfer the files