i like to use ubuntu mostly
i ran it on my old 733 mhz inpiron 4100 pentium 3 before i got my macbook
it ran amazingly! the only problem i had was getting my netgear wireless card to work, but that wan't that bad
slax isn't that bad to run when you're learning, it's free (actually most are open source) and doesn't need to install to a partition on your hard disk