On my hard drive (640GB) I have 3 partitions, one being time machine, the other two being storage. The drive is in Mac OS Extended (Journaled). I need it to be in FAT-32. Can I change formats without erasing? If I can't, how can I back up the 640GB of data on the drive when I've got a 120GB computer that's already full? And can you partition a FAT32 drive?