I wanted to try out Xubuntu on an old Dell Latitude L400 notebook because its Xfce X11 windows manager is tuned for low-RAM systems (the L400 has 256MB RAM). Unfortunately, it only managed to display half the screen making it unusable. So, I left Puppy Linux running on the Dell.
Sorry for the blurry image. I took the photo with a camera phone.
It is possible to run Xubuntu on a Dell L400. Right now I am using my L400 (PIII 700Mhz, 256 RAM) with Xubuntu. Try to install it with the “Alternate install CD”, and not with the Live-CD, available on most mirrors. In my case, everything but the Xfce-battery-applet works great.
I have one running Xubuntu just fine. What version are you using?