Power is 12V, I believe. There are SLAs that will do the job, and there are also a good number of Li-Ion packs out there that will deliver voltage.
If you connect it to the PCI card, it's self powered through the proprietary firewire. Only for the desktop interface, unfortunately.
One thing to reiterate before you "hammersnipe" one though - the Multiface does not have any preamps built in. So if you're not feeding it line level signals you'll need a preamp on those channels.
Way back when, before I had the multitrack setup I have now, I did run the Multiset without any preamps. If you're running at 24bit you're mostly OK with mic level signals because they can be boosted with minimal noise in post. You have no input level control though.
I did a number of live shows like this though, so it's not really a problem. It's not ideal, but it's not so bad either.
Dirk