For P2P networking, the best bet is to have a networking card in both PC’s and use a crossover cable. A crossover cable can be purchased from most computer stores for about 15-20 USD. This allows both PC’s to communicate at whatever speed the card is(10/100.)
Assign one computer the IP address of 10.1.1.0 and assign 10.1.1.1 to the other. Share a drive and you’re off!
Regular ethernet cables will only work if there’s a hub in use between the two PC’s(PC to hub.) You’ll still have to assign the IP addresses.
I keep a crossover cable in my laptop bag for just such an emergency. Works without fail every time!