The difference is that LimeWire uses the open gnutella protocol and Kazaa does not.

LimeWire also offers a free version which is exactly the same as the PRO version (except for a little bundled software).

__________________
Morgens ess ich Cornflakes und abends ess ich Brot
Und wenn ich lang genug gelebt hab, dann sterb ich und bin tot

--Fischmob