Have you changed the import path to read the hand history files written by the browser Party software?
Are the hand history files being written as you play? If not, try disabling the 'save hand histories' option in the Party client and then enabling it again - IIRC I had a problem getting it working when I first tried it on Lion and that got it working.
The default path should be:
/Applications/PartyGaming/PartyPoker/HandHistory
If hand histories are being written and you think everything is set up correctly but the hands aren't importing please restart PT3 and play a few hands at a single table. Attach the PokerTracker.log file to a
Support Ticket along with the hand history file for the session and that should let us see what is going on.