Some of the featured software in Ubuntu v5.04 include Gnome 2.10.1, X.org 6.8.2 and Firefox 1.0.2. You can read about all the changes in the Release Notes for v5.04.
If you’d like to try both desktop environments, you can simply install Ubuntu and then issue an
apt-get install kubuntu-desktop to install the necessary Kubuntu files, allowing you to choose which DE to use at login.
If you’re curious about Ubuntu Linux, but don’t want to install it on top of the operating system you already have, you can download a “Live CD” from the link above, which will allow you to boot from the disc and try a version of the OS that lives completely on the CD-Rom. With this you can try the distribution out on your particular hardware with no changes made to the underlying system.