Bootable External USB/FireWire Hard Drive?

[Matrox462]

I have an Acomdata 80GB USB 2.0/Firewire external drive, and I was wondering if it'd be possible to load an OS on it and boot off of it. I know it's probably just a question of if my BIOS can support that kind of thing or not, but frankly I'm not quite sure if it's even possible or if it's worth the hassle. And no I'm not doing it so I can plug the drive into any system and boot the OS on it, I'm doing it cause I was thinking about installing Linux on my primary computer, and I don't want to mess with my partitions as I have a 'back up' partition, which is my *only* copy of WinXP that came with this computer lol, so if I mess that up, I'm kinda out of an operating system and the drivers that came with my computer. Also, if I was able to dual boot Linux (external drive) and WinXP (internal drive) what would happen if the external was powered off or unplugged? Could XP load fine alone? If it is indeed possible to do, I just need a little direction as to how to go about doing it. Thanks!