Do you have a switch user option when you log out. That will do it. You can also use "xinit -- :1.0" and then launch a new windows manager in the xterm.
The first method if available is preferable. There could be contention problems is your run the same desktop manager in both windows, and if you use xgl/compiz in the an initial kde session, running "start kde" in the second might screw up the first. ( I just tested it out and that is what happened. )
You should add your distro to your profile so you can get distro specific advice which is usually best.
Sorry, I brushed over the part of there being two distinct users, so there may not be the same problem. I ran my quick test as the same user.
You might want to google for "multi seat linux". There are some articles on configuring X windows to run with more than one user at the same time, each using their own mouse/keyboard and monitor. It works better if you have different video cards instead of using a duel head setup, but it still might be worth a try. The article set up a computer with 5 seats. Something like that might be very useful for a small internet cafe owner.
Last edited by jschiwal; 03-31-2007 at 11:51 PM.