Kazaa uses a closed protocol (I really can't remember the name), and I don't think you can find Linux applications to support this protocol. However, there are a number of clients supprting gnutella network. LimeWire mentioned before is one of them.
I presonally suggest Mutella. It is a full-scale client, abnormally fast, and so far I got the best results with it. The user interface is text-based, but it takes only several minutes to get used to it. Also, if that bothers you, there is a web interface that can be run against Mutella.
There is also the supporting dosumentation there.
Give it half an hour - you'll never want to use another client again.