GFE
GFE stands for Game File Extractor.
It’s an interface to allow you to install custom third party content (eg, maps, skins etc.) in to Unreal Tournament 2003 & Jedi Knight 2. I did have working versions for UT2004 & Jedi Academy, but I’ve lost them now. Sorry 
Screenshot 1 - zip file extraction
Screenshot 2 - install from cache
Screenshot 3 - installed files
Screenshot 4 - search for files
Screenshot 5 - installation log
The UT2003 version was 4th place in Phase 1 of the Epic Make Something Unreal Contest tools category!
Download GFE for Unreal Tournament 2003
Download GFE for Jedi Knight II
The above versions of GFE require the Microsoft .NET framework installed, it is approx a 20 MB download. Before downloading GFE please make sure you have installed this.
I created a version in Java so I could use it in Linux. I called it GFELite, because it’s has less features - Download here. An overview of how to use it can be found here.
GFE has also been ported to Ruby, it works with both UT2003 & UT2004. It was written primarily for Linux, but also works on Windows (apparently, but you may have to compile it yourself). Please visit the RubyGFE homepage for more information.