What, a P1 200 is old? Dude that's my coffe table box. Middle-aged maybe, but not old. I'm running Slack 7.1, BSD 4.4 and LFS 3.1 off of one of those. Though honestly you could probably find another stick of either PC66 sdram or EDO (depending on what it runs), for something like $5-10 and really crank its ability to perform with any of yesterday's distro releases. Then again, even spending $5 on an old machine always seems like a waste.
Anyway, like the other guys said, all the modern releases, even the ones that tend to bloat like RedHat and Mandy, will still run comfortably on the pentium series. If you really want to try and get the performance increase by going back a version or so, it would probably be best to try any of them that used the 2.2.x kernel series: Redhats in the 6.x's, Mandrake through the 7's, Slack 7+7.1, Debian's 2.2r3 Potato (which is still their current?), and I really don't know much about the Suse's's's because Live Evals make me twitch. These all ran XFree3.3.x, which is a little more lightweight, and had prior versions of Gnome and KDE that weren't built to romp through 64Mb Graphics cards.