[dnanian]

I'm not quite sure why you wouldn't want to upgrade the firmware in a drive -- it's always a good idea to keep the drive current with its current firmware, since they tend to fix bugs in the drive.

Anyway, I've used the LaCie Little Big Disk as well as some of the smaller OWC drives. It's important to note that bus powered drives of larger capacity can sometimes draw too much power and cause problems...

Anyway -- if you want to be able to start up from a drive, it's pretty important to have enough free space for the OS's temporary, swapfiles, etc. So, don't cut it too close. But, you can partition appropriately and use the rest of the drive space as desired.

The one that boots is the one you select to boot.

You can back up two computers to the same disk -- just partition... and choose the partition to boot from.