ok so i just got my new MBP last monday... Leopard came in the mail today i installed all went well....i have had a 500GB western digital external HD for a few months now and have been saving stuff to that instead of my Pcs hard drive as one would imagine i have alot of stuff on there but everytime i try to use it as my backup drive for time machine it tells me i have to erase everything on it...as you prolly already guessed i dont want to loose my stuff...is there any way around this?