Puppy Linux, will run in about 100 mb ram with apps aboard, so very fast.
Mediapup, a variation of that will convert it into a video editing system, both will load off a CD or small thumb drive when needed, or coexist with other OS's -- if you're interested in Linux at all.
I use an even lower grade machine to act a as a console for a CNC foam cutter I built. Best performance is with DOS software (TurboCNC), though Windows based CNC does work, too. But the drive is much smoother with the DOS driver.
A guy once asked me if he should get a rowing shell to get exercise in. I said no, get a Sears aluminum skiff and add cinder blocks, and short oars. Then you'll really get exercise.
Fun in computing can come from overcoming limitations, not just buying the fastest and the best (and therefore next years has-been) devices. But using ingenuity to make something unusual with cast-offs.