Yeah, definite push for Gentoo... although.. for first time.. maybe not for you.
I'd stick to SuSE, Fedora, or Mandrake.
Although, with your old(er) machine, you may want something like Gentoo or even (*cringe*Debian*cringe*
).
Anyways, DamnSmallLinux (
www.damnsmalllinux.org) is pretty cool. 50 meg bootable image (burn it to CD, copy it to USB drive, whatever). Has quite a bit of stuff, too. (Yes, I know it's based on Knoppix which is based on Debian).