TL;DR version bellow. just need a distro that meets those requirements well.
I have an old Dell Dimension 3000 that has been out of comision for a while. i haven't used it in forever. I just installed Ubuntu on my laptop for the first time last week. So i thought, why not put it on the Dell and rehabilitate it? its got a virus-riden XPHome on it. my plan is to wipe the HD to kill the virus (and all the old files i don't need anymore), reinstall XP, and then get a Linux distro to Dual-boot on it. This will more or less be my guinea-pig machine for experimenting and learning more about computers. I don't have the specs at the moment, but its carrying 2 Ram sticks totaling exactly 512 MB. i know this wont run Ubuntu well, and id like to try a different one anyways.
so, what distros do you think meet these requirements:
1. good to experiement with.
2. will run well on about 512 MB of RAM
3. still has a GUI as well as the CLI (i'm no where near used to the terminal.)