Sticking with older hardware may mean that you miss out on the possibilities offered by later kit and being able to boot from external optical and hard disk drives was something of which I learned only recently. Like many things, a compatible motherboard and my enforced summer upgrade means that I have one with the requisite capabilities.
There is usually an external DVD drive attached to my main PC so that allowed the prospect of a test. A bit of poking around in the BIOS settings for the Foxconn motherboard was sufficient to get it looking at the external drive at boot time. Popping in a CrunchBang Linux live DVD was all that was needed to prove that booting from a USB drive was a goer. That CrunchBang is a minimalist variant of Ubuntu helped for acceptable speed at system startup and afterwards.
Having lived off them while in home PC limbo, the temptation to test out the idea of installing an operating system on an external HD and booting from that is definitely there though I think that I’ll be keeping mine as backup drives for now. Still, there’s nothing to stop me installing an operating system onto of them and giving that a whirl sometime. Of course, speed constraints mean that any use of such an arrangement would be occasional but, in the event of an emergency, such a setup could have its uses and tide you over for longer than a Live CD or DVD. Having the chance to poke around with an alternative operating system as it might exist on a real PC has its appeal too and avoids the need for any partitioning and other chores that dual booting would require. After all, there’s only so much testing that can be done in a virtual machine.