you don't need to reinstall it as your own user.
don't use sudo before it, open a command line console, and copy/paste:
/usr/local/games/tremulous/tremulous.x86
it should also be in your "start" bar, or the foot bar, or whaterver the hell gnome calls it. Under games.
The first time you run it, it will create the ~/.tremulous directory which holds your configs. ~ signifying your home directory.
Make sure you are running it as the same user you logged in as, do not use sudo or su to run the game. If all else fails, open a console and type
id && ls -l /home/
and paste that here.
ODDity, installing it this way installs it into /usr/local/games/tremulous for multi-user use. It is perfectly usable as an install method, and I have done this many, many times. New files/additional files will be written to the users ~/.tremulous directory, the way it should be. As we don't know if this individual has brothers/sisters who will fight over the use of the computer, and I don't care to try to revert this if that is the case

, it seems a prudent way to go about it.