came across this post when searching how to restart the xserver from the command line - I'm rarely at my knoppix machine and do most things from my win laptop via SSH. When I ocasionally need a GUI, I use VNC4. This works fine, except from time to time (I leave the knoppix box on all the time) the xserver is unresponsive :(

so this is the command I found that does the job for me - it restarts KDM (which by Knoppix default we're using in preference to XDM) which restarts the xserver
Code:
sudo /etc/init.d/kdm restart
this may not be the most elegant/correct way but it works(tm) and I thought it might be useful for others...