my recently new MBP running snow leopard froze a few times in a row and eventually wouldnt load past the gray screen. I booted from the install disk and disk utility says i have an invalid node structure. How do get all of my saved files to an external hhd before doing anything to my computer???? Im not too familiar with backing up things so I dont know what im doing. Once everything is backed up what do i do to fix my MBP? Thank You!!!!!!!