I have every Mac OS the B&W can run installed on it right now (different partitions of one drive.)
Wow, that's insane!!

How many do you have, eg do you count 9.0, 9.2 etc as different versions, do you have all the server variants or just the clients, do you have the Rhapsody-like ones like OS X Server 1.0 etc? I've always thought multi-boot can't be very practical on a Mac though, 9 and X is fine as on mine it seems to default to X and if you want 9 you just hold Option on startup, but if you had several Xs for instance, there's surely no way to choose between them on startup like there is on a PC, you'd have to boot the last one you used first and then reboot from Startup Disk into the one that you wanted?