To use those themes you need Superkaramba. Do a google search for the homepage.
I had trouble comiling the latest release on RedHat 8.0 but the previous version worked just fine.
The default taskbar is called kicker. Killing kicker is not usually a good idea since you lose several pieces of Kde. It will still work, you'll just be missing portions of it.
If you're dead set on it, run:
bash2.05$ ps -aux | grep kicker
then kill the pid returned
Right now I keep kicker alive as only a taskbar that is on autohide on the top center of the screen.