Xubuntu is okay on old machines and I wanted to try it but it can't detect most of my hardware for some reason and wanted to format my whole hard drive on one of my machines... Another bad experience on someting Debian-based for me, but if it works for you, then it's a good choice and so is DreamLinux.
A good surprise on an old machine was Yoper. I had a major breakdown on my main machine over the week-end and I had to find an OS with graphical interface that worked well on my old PentiumII 300MHz with 64 MB of RAM to fish for some information to solve my problems. Xubuntu didn't work for me, as usual, so I tried that Yoper CD I had and it worked fine. The trick is to do a base install and install the rest of the packages afterwards. It's rather fast with Xfce and even KDE works, although it's very slow. The main inconvenient I found is that their repos are a bit limited.
Ma philosophie d'apprentissage : essayer, et si ça casse, essayer de réparer.
My learning philosophy: try it, and if it breaks, try to fix it.