I have USB cable I used for such purpose... worked even between Xp <> W2K. Was cheap too... can't remeber the name right now, but there are many manufacturers that do these "USB network" thingies.
I've even seen some 'universal' USB cables that snap on a regular Ethernet RJ45 jack on both sides, but at that point it really just becomes a cross-over network cable that happens to run over a wirepair that's part of a physical USB cable.