There will NEVER be a totally equal alternative to Napster but, like Supra says, Bearshare is about the closest although not for an uninformed user. You should educate yourself about packets and how they work. If not, you'll just slow down the whole network and get some people irate. Also I don't like what I've been hearing about the Gnutella worm that is a very real and serious risk if you don't know how to defend yourself.
Oh, and let's not forget, I don't think you can choose a bitrate for your songs either! Most are available at only 128kbps which is VERY unacceptable to me, at least.