CANNOT KILL X: X become Zombie and REBOOT must be done !!!

[Alessandro Torrisi <alessandro torrisi eurone it>]

Please help me ! I have this problem from FC2 and now with FC3 the same 
thing !!! I was setting up the screensaver and tested it twice when mouse 
started to become slow very slow ! KDE was not under my control, so I 
connected with a notebook to SSH.

I saw the process X in a ZOMBIE status with a CPU usage of 90% !!!
Why ? Why cannot kill zombie processes ? What I have to do ?

Alex.