[dnanian]

First off, you're right in one of your questions: I think it's a mistake to put a backup on the same physical device as your data. In the event of a hardware failure -- the most likely catastrophic failure will be your drive -- you'll have no way to recover. This is a big mistake.

So, if you want to keep your data on a FireWire drive, you should have a separate FireWire drive for your backups.

I'd then suggest partitioning the backup appropriately to give each backed up source volume its own destination volume.

I'd really boot from your PowerBook and -- if you must -- use one (data only) drive for storage, but always boot from the PowerBook. Then, have a second drive onto which you place the various backups.