Wiki.ubuntu.com/Xubuntu states - The aim of the Xubuntu community project is to provide a nice Ubuntu desktop experience (even on older hardware) by using Xfce4 as the desktop environment and GTK+ 2 applications wherever possible. Xfce4 has been supported in Ubuntu's universe by the MOTUXfce team since Hoary and Breezy. For Dapper we want to go one step further and make Xubuntu a sibling of Ubuntu, Kubuntu, and Edubuntu by having install and live CD images generated for it. We haven't decided on a release date, but it should be as close as possible to Dapper's and should use the latest stable Xfce 4.X code (hopefully 4.4 will be release by then)

OSDir has some nice shots of Xubuntu 5.10.