i recommend you try HIARCS with the Sigma interface, very strong program, i believe it came in 2nd place right behind rybka in the world chess championship for computers. here is the link to theyr site if your interested
http://www.hiarcs.com/mac_chess_hiarcs.htm
hope that helped my friend.
I cant find Fritz on mac. Is this even available? If not are there any good programs for mac that are comparable?