Head on over to http://www.kubuntu.org/ or http://www.ubuntu.org/ to get the freshest drops of the slickest OS out there. As always you can boot it off a liveCD if you want to try it our with NO changes to your existing OS. If you choose to install it, it dual boots nice with any Windows, and as long as you install it second, it will add a nice boot loader for you that gives you an easy menu to allow you to chose which OS to boot to.
Check it out today!
The kubuntu drop comes with KDE 4 or 3.x, depending on if you are feeling adventurous or not.
There are tone of new features out in the latest drop, all listed on http://www.kubuntu.org/ so check it out.