Today I searched for a good freeware video editing tool for Linux and found http://www.openshotvideo.com/.
It is perfect for converted demos of Nexuiz to implement music, a spashscreen or whatever else is your desire.
You also can convert it right into the YouTube format, even the HD.
It is based on various timepaths, you can drag and drop each item such as movies, music or pictures.
I guess its one of the most handy and slim video editing tools for free out there.
And just for Linux
Installation is possible with a .deb file and there is also an instruction to install it per console.
http://www.openshotvideo.com/
have fun,
greetings,
sardine