Well, it all depends on how much ram do you have and what are you going to use it for...
The problem is that easy distro's(Red Hat, Mandrake, SuSE) do not run fast on old comps,
fast distro's like Slackware and Gentoo are hard to use if you never used Linux.
RedHat 9 will run on it, but not very fast, but if you have more than 64mb it's not a problem.
There a distro called 'Vectorl Linux' it basically Slackware with some graphical tools, it's
not the best distro around but it works well on old comps. It's also small, 1CD only 400~mb
The main thing that I don't like about it is that it does not come with KDE.
What you could do is install Vector, use it untill you understand how to make it works and
then jump to Slackware.