Limewire supports the Gnutella protocol and Kazaa is on the Fasttrack network. The two are not compatible. As far as I know, there are no Fasttrack clients for Mac. The only muliple protocol client I know of is iSwipe, which is available for OSX. It supports Gnutella, Hotline, Opennap, FTP and Carracho (but not Fasttrack). Here's the link:

http://hillmanminx.com/