On OS X (my imac) I just trashed the folder with all the SC2 beta files on it. Then I installed SC2 retail on my hard drive from the dvd and that worked just fine. So I think trashing the SC2 beta folder is your best bet. And I checked around and the beta does not leave any little hidden files anywhere you need to worry about. And you already posted this question here: http://www.starcraft2forum.org/forums/showthread.php?t=16464&page=2 No need to post it multiple times.
sorr y for the double post, just trying to get a fast answer... cool and thanks i'll do that... can't wait to start playing