You may want to try Xubuntu. It runs just as well as Ubuntu but uses the lightweight Xfce desktop environment as opposed to Ubuntu’s GNOME desktop environment. I don’t recommend any of the 8.04 releases because it’s impossible to add new users or manage groups using the Users & Groups GUI program. Hopefully Xubuntu 8.04.1 fixes that. If it does, then I’ll recommend Xubuntu 8.04. If you’d like an even lighter desktop environment, then go for Linux Mint 4,0 Fluxbox Community Edition (uses Fluxbox, which is VERY lightweight), OzOs (uses the latest builds of Enlightenment E17, which is very lightweight but as a very nice look), or gOS Ultimate E (remastered version of gOS Rocket E that I have on my laptop right now...I love it).
I have since installed Mint Elyssa. It works pretty good. I have the PC in the basement and haven’t had a lot of time to hook up speakers and test it out. It took a few days to get the wi-fi up and running.