I currently have a 20gig usb drive booting BT3. I was wondering how i could dual boot BT3 and Ophcrack on it. (And possibly a third OS later)
Tutorial for booting ophcrack from usb can be found at pendrivelinux.com
Divide the hard drive into multiple partitions, at least one partition per OS, and use a bootloader to choose which OS to use at startup. Both Lilo and Grub would be good candidates for this task.