I have an external HDD which is a 320 gb SATA HDD. I want to replace my 120 gb HDD in my MBP but before I go buy a new HDD, wanted to see if my external HDD would work. The catch is that the external HDD was my old HDD from my HP laptop. Could I simply reformat it for OS X or once it's gone Windows can it ever be used for anything else? I suppose I could just remove my existing HDD and put this one in and see, but if it's a waste of time, I'd rather not. Thoughts?