You might do better with a base install of Debian GNU/Linux and then add stuff like xserver-xorg, xfce4, iceweasel, and anything else you think he might need. Also be sure to add the contrib and non-free trees along with the main tree to your apt repositories if you want Flash and Java installed.

I did this on an old Compaq Presario with a K6-300, 64 MB RAM, and a 4 GB hard drive and was quite surprised at how useful it was. Mind you, it did slow down a bit when accessing "web 2.0" sites like MySpace and the like, but it shouldn't be too bad on that Dell. I even had space to spare on that 4 GB, although not too much...