Automatic Shut Down When Battery Low?

I'm new to the Mac scene. I was wondering if there is a way to set my PB to shut down after the battery gets down to a certain level. I've looked around for this option, but can't seem to find it. Any help would be appreciated.

on a note of personal experieance, i've run my bat down to the point when, yes, it automatically shutdown/slept. couldn't wake it till i plugged it back in, BUT once i did, i started right back up where i left off.

I've run the battery down until it shut off.... but if you wait too long after that before plugging in, the battery can die completely and you'll lose not only your current status but also the system time, etc.
Anyways, I believe there are some AppleScript commands you could use to accomplish your purpose (maybe?)