If for whatever reason you can't double click on a *.umod file to install a mod you can do the following:
1. Place the umod file in your unrealtournament/system directory.
2. Open up command window.
3. Change to your unrealtournament/system directory.
4. Type the following command: "setup install comsic200.umod" - be sure to replace cosmic200.umod with the name of the mod file you are trying to install.
5. Follow the directions in the installation window.
If you know how, you can associate this filetype to "setup install "%1"" so that you can doubleclick umod files from now on.