Cpu usage by X

[DB]

Hi All!

Anyone able to give me an idea where to look......

Sometimes when I start my desktop, System Monitor tells me that "X" is 
running at max CPU %-age.  Other times, "X" is 4th or 5th in the list (I 
selected the CPU column to put the highest users on top), using 1 or 2 %.

So, my question to you all:  What is "X" doing & how can I stop it doing 
whatever & keep my CPU chip cool?????  BTW, I have no idea what X is!!!  
I've tried killing it & that usually kills my desktop; just now killing 
it caused the system to restart.

My system: uname -ar
Linux Fedora-Blue 2.6.30.10-105.2.23.fc11.i586 #1 SMP Thu Feb 11 
06:51:26 UTC 2010 i686 athlon i386 GNU/Linux

running F11 & kde installed from the F11-KDE-Livecd.

As ever, Thanks for any help!

Dave