If you're looking for a P2P client for OS X, I highly recommend Poisoned. It's a free, open source application that works seamlessly with both the FastTrack & Gnutella networks, and there's OpenNap & eDonkey support in the works. It's got a slick, fast interface, and integrates nicely with iTunes, importing downloaded files and (optionally) deleting the original.
There's no installer, and the 1.66 MB download expands to a mere 5.3 MB footprint, so give it a whirl.