This might be a dumb question but I'm not so well-versed with hardware issues. I know how to make bootable DVDs and USBs for reinstalling OS on my MBP (I'm trying Lion in particular) and was wondering if it would be possible to use an external HD for the same thing. I have no DVDs or USBs with enough gb for the install, but I have a 350gb HD which I use for all of my movies/tv shows. If I make a bootable disk with the HD, will it be able to return to its original format after? Again, this might be a really stupid question, I just can't take any chances with my external.