10.3 runs fine for me. G3/400, 512mb.
As with all things, mileage varies. I had to work with 10.2/10.3 and Server 10.3 on old PPC macs in a previous job and it was a total pain. Unresponsive, crash prone and to add insult to injury, the server edition totally screwed up it's own filesystem one morning and couldn't be recovered. The disk itself was fine. Were it not for a regular backup, we'd have been up the creek without a paddle.
