There is a program called Mac Poker Pro made by Open End Software that does about the same thing as PokerTracker, but it does not put the info on the table (like PAHUD); rather, it puts it in a separate window on the desktop.
http://www.openendsoftware.com/macpokerpro/
Unlike PokerTracker, however, it does update automatically; and I found it easier to use. The last time I used it, it did not keep track of as many stats as PokerTracker. But that was over a year ago.
Another alternative (if you have an Intel Mac) would be to break down and install a copy of Windows on your machine and play poker on the PC side.
HTH,
--klez