I just came on to post this too.. I beat it awhile ago on PC but fortunately I bought it on steam so now with Steamplay with new achievements, I must play it again on OSX!! This is amazing stuff.
Looking at the game after loading it, there's in-game achievements along with the steam ones, so I dunno if you can get a separate patch or what since mine was auto updated on steam. So I don't know if you have to go to popcap site to look for a patch or what.