If the username you want to use is games, then put the following in your startup scripts:
Code:
su - games -c /usr/games/ut/launchit
I don't know where Debian keeps its startup stuff - have a look for one of the following:
Code:
/etc/rc.d/rc.local
/etc/init.d/boot.local
/etc/rc.d/init.d/rc.local
If the game requires specific environment variables you may need to modify /usr/games/ut/launchit or create a wrapper script that sets the variables before launching /usr/games/ut/launchit.