If you want to run linux, first you need whats called a distribution. It includes:
A kernel
A User Interface
Assorted Aplications
The kernel is what linux IS. The kernel is what Linus writes, and its job is to be the layer between your hardware and everything else, so nothing has to be written specifically for certain hardware to run on linux. The code is genius.
KDE itself doesnt support standards set by opendesktop, and I would reccomend GNOME anyways, because Im biased. In the next few versions look for a lot of new features and integration with GNOME and other programs.
As for a linux distribution, I highly reccomend you go to
http://fedora.redhat.com and read up a bit. If you are serious, download some ISOs, and create a dual boot computer. The process is easier than the windows installer, even a kid could do it, and Ive never had it fail.
Now that you have a dual boot, spend some time in it, learn the operating system. Linux distros are usually focused with coding and such, and come with a lot of programs for that, so for the normal user it may not be as useful, but there are some alternatives.
Best part: any software worth having is free!
Come on to #tfp (see link in my sig) if you want some help in real time, theres usually someone in there who is knowlegable about linux.
Good luck.