Puppy is a good one too, though its wireless support is pretty craptastic, most machines that you are putting it on wouldnt have Wireless anyway. I put it on an old Gateway PIII 600 with 384MB of RAM and it would boot up to about 85MB used. Hard wire NIC and everything else worked right out of the box, just had a hard time getting a PCMCIA wireless card to work, and stay working (it did work, just not consistently). bit that could have just been the one i was using, others may be a little easier, who knows.
Puppy would SCREAM on that machine. The PIII 600 i had it on had no problem running Firefox with a youtube video in it while surfing other pages at the same time... no stutter.