I think you can use the Alternate Install CD to install the Xubuntu desktop if you can connect to the internet. You would install the 8.04 Server (base install -- I think it is a menu item on the Alternate Install opening menu). The Server install is just a command line system. Once it is installed, you might have to set up the internet connection using command-line tools. Once you have an internet connection, you can install the Xubuntu desktop by
It will fetch the packages over the internet, and install them. Once they are installed (might take an hour or so) enter startx or reboot to get a desktop.
sudo apt-get install xubuntu-desktop
Of course, this depends on being able to connect to the internet. Wired connections are usually a sure thing, but the wireless might not work easily. Do you know what kind of wireless card it is?
Anyway, installing the Server edition of 8.04 is probably safe, and at least you would have a command line to play around with.