You just need the right cable like these guys are saying. Any shop should be able to sell you one, Mac, PC, whatever, it doesn't matter but it's got to be a crossover cable, not a regular ethernet cable. I got one from my Mac shop and it was exactly the same as all the other cables, only it had "-X" at the end of the product number.
You then set the AppleTalk control panel to use Ethernet, turn on file sharing, and you're away. Each computer should show up in the Chooser of the other.