To achieve this you need a script to start urban with. here is mine:
#!/bin/bash
#
# Urban Terror separate X starter for linux by RifleRat-NoSkill
# Tested under Ubuntu & Kubuntu 7.10 & 8.04
#
# We start another X server, pipe anything not returned by ut to /dev/null (otherwise
# something presses enter until we kill the terminal we executed it from.
#
# You can swicth between your desktop and UT with Ctr+Alt+F7 and Ctr+Alt+F8 or F9
# regarding to your system settings
#
# Please check the path to your Urban Terror installation and correct it below
# if necessarry
xinit /usr/local/games/UrbanTerror/ioUrbanTerror.i386 $* -- :1 > /dev/null
save this script as e.g. x.urt and give executable rights to it
in order to get it work you need two additional things --> 1) you should allow yourself to be able to start an X session
on display :1
2) edit /etc/X11/Xwrapper.config
let's do it
run xauth in a terminal.
it will prompt you with this:
xauth>
type
xauth>list
it lists your magic cookies for the xsessions, similar like this (it is mine):
sipiatti/unix:0 MIT-MAGIC-COOKIE-1 00cff1b540617cd449b6b4053a3dcbef
localhost.localdomain/unix:0 MIT-MAGIC-COOKIE-1 00cff1b540617cd449b6b4053a3dcbef
your is different, that is normal
now you need to add your magic cookie to display :1 do as the following
xauth>add :1 MIT-MAGIC-COOKIE-1 00cff1b540617cd449b6b4053a3dcbef
run gksu gedit /etc/X11/Xwrapper.config
you should see this:
# Xwrapper.config (Debian X Window System server wrapper configuration file)
#
# This file was generated by the post-installation script of the x11-common
# package using values from the debconf database.
#
# See the Xwrapper.config(5) manual page for more information.
#
# This file is automatically updated on upgrades of the x11-common package
# *only* if it has not been modified since the last upgrade of that package.
#
# If you have edited this file but would like it to be automatically updated
# again, run the following command as root:
# dpkg-reconfigure x11-common
allowed_users=console
nice_value=0
change the allowed users to anybody like this:
allowed_users=anybody
that's all.
now you can type /home/youruser/pathtoyourscript/x.urt
and a new X will start and only urban terror will run on it
you can switch between your desktop and urt with Ctr+Alt+F7 and Ctr+Alt+F8 or F9
Good Luck!