Well, it depends on what you want on your BootCD. If you only want to be able to delete some incredibly nasty spyware that won't delete, then you don't need much. If you want to run 10-15 applications from memory, that's a different story. By the way, for OS issues, I'd just recommend you image your HD with Acronis True Image when everything is ok, so you can revert to it when things get rough. Or use Deep Freeze to freeze the state of your HD and burn to CD/DVD / save to another harddrive when you don't want something erased from a reboot. Off-topic but just for reference.