must... not... must... resist... urge... to... take... stab... at... macs...
AFAIK, since macs are just crippled *nix boxes, any nix client should work. (sorry i had to have a dig somewhere!
)
A branch of emule for nix is called aMule:
http://www.amule.org/
And presumably, Mldonkey:
http://mldonkey.org/
That's your client options, or at least the decent ones.
aMule is relatively simple to setup, its a port of emule. MLDonkey is a bit more nixy.
edit:
forgot about lPhant:
http://www.lphant.com/
I think you can use mono and use it, can't access any of the homepages from work.
