I'm not a Mac user, but I've been planning on getting a Mac and have done a fair amount of research. You should have no problem running Windows apps on Parallels or Boot Camp.
The main benefit of Parallels is that you don't have to reboot in order to run your poker software. However, it costs $80, whereas Boot Camp is free. Besides cost, there is no decided advantage to Boot Camp. If you're a heavy 3-D gamer, some of your games may not be supported in Parallels, but Parallels 3.0 has made a lot of advances in 3-D gaming.
You can utilize both Paralles and Boot Camp on the same Mac. This
tutorial explains how. I think this is your best bet. I would start off with Boot Camp because it's free. Then if you find having to reboot into windows to play poker tiresome, you can always fork over the $80 to get parallels.
If you're looking for more information, you'd be better off posting on a Mac forum or in the
Parallels forum.
Also, I would hold off on getting PokerTracker,
Holdem Manager will be coming out soon and it looks like it'll be awesome. Plus they'll be a free beta period so you can test it out and see if it's worth it.