you can do this several, ways depending on what you have. i remember using a 9 pin din serial cable back in the day with 9x computers. windows back then came with a utility for doing it, but im not sure if it came with any of the NT5 platforms.
an easier way to do it would be thru a network. if you have a switch or a router, simply plug them both in to it, make sure they have the same workgroup (assuming you use windows) and then they should be visible to each other over network neighborhood (my network places). then simply right click on whatever folder you want to share, and click on "sharing and security".
if you do not have a switch or router, make or buy a crossover ethernet cable and then plug each end of it into the ethernet port of the two compys. this basically makes a direct network connection. then simply do the same thing as above with sharing, workgroups, etc.
of course, there is always burning cd/dvd's. also if you have a hard drive laying around you can purchase a external drive kit for less than $30 instead of paying a couple hundred for a new one. alternatively, you can take the spare drive and just stick it in the one computer, copy, then stick it in the other.