I got some good advice about deleting dmg files so I thought I'd ask about the Previous Systems folder on the HD. I recently tried to delete too much and had to reboot from the disk. It put a folder named "Previous Systems" on the HD and its taking up 7.72 GB. I'm back up again and up to date. Everything seems to be working. I know I screwed up before so I'm asking here before I delete too much again.