I just got Ubuntu installed on Clare's laptop. It only has 256meg RAM that's shared with the video card so it was running like a pig even with XP. Honestly, who manufactures a system with only 256meg of RAM? It was a battle because the Ubuntu and Kubuntu livecds require at least 256 to run, and they were both failing. Xubuntu started up, but ran like a dog.
Any of the three versions will run on systems as low as 128mb, you just need to use the standard installer rather than the livecd. Only trouble is, because I'm stupid, it took me a while to figure that out. Anyway, I downloaded the alternate installation cd and eventually got it happening, and now I am the smartest man alive.
Also, the kde desktop looks pretty cool except for the fact it uses Konquerer. If there was a version of kde that used Nautilus and Firefox I'd be sold. Nevertheless, I might check it out in the near future, since it looks cool.