Are you doing it with a CAT 5 line (RJ-45 jacks and plugs) but without a hub? If so, some of the lines need to be switched around (into what's called a "crossover"), and that can be done at the jack/plug junction. ...sorry I haven't done the peer-to-peer thing in a long time and don't have a diagram. But you should be able to find a peer-to-peer wiring diagram on the Web, somewhere. Just try keywords like, "peer-to-peer," "CAT 5," "RJ-45," "diagram," "crossover" and so forth.
This could very well be your problem. I have networked laptops together doing this, (One with Win2k and the other with Win98se) and it is easy. You can find crossover cables on eBay for 3 or 4 bucks and all you need to do is plug the end of the cable into the NIC on each machine....and Whooppeee!