Hi I am a big fan of Ubuntu. It got me really interested in Linux and gave me the push to leave Mac and Windows behind. I had Ubuntu 9.10 running on a Samsung A10 1.1Ghz Duron and loved it, then the laptop died. I then was given an IBM ThinkPad 600 and after running a few ' lightweight' distros have been quite impressed with Xubuntu 9.10 on it.
Haven't actually tried any lower-spec distributions recently, but I did stumble across Lubuntu recently:
It's a Canonical-sponsored project based around Ubuntu and LXDE.
Might also be worth a look,
Peter.