For some reason I’ve never quite grasped, Kazaa is what most people seem to think of when a file sharing app is suggested. The free version is full of spyware, the pay version still has a little (IIRC), and it uses the same networks as the rest of them do.

So dump it! Try Shareaza — it’s free (beer AND speech), has no spyware at all, and the latest release is open source (GPL), too. It can access the Gnutella1, Gnutella2, and eDonkey networks, and was perhaps the first client to offer swarmed downloading (not sure if competitors do that now, probably so), where you only download a few bytes of the file from multiple sources, so the file comes together bit by bit, and as soon as you download a bit of it, someone else can download that bit from you, which really speeds things up tremendously because you’re not limited to people with the completed file, and you can download bits and pieces from a dozen people at once. So try it, I think you’ll like it. :-)