A few things I should clarify about my earlier post:
I'm writing this for fun. I don't expect this game will come to anything much at all. If it's fun and playable, I might release it and try and get it packaged for a few different distros. My main motivation in writing the game is for me to improve my own programming skills.
I'm using Qt4 and qDevelop, nothing else. Qt4 is simply the best cross-platform C++ library I've ever seen, and qDevelop is a nice cross platform IDE that does everything I want it to.
Right now I have collision detection going, although it needs a few tweaks for fast-moving objects (like bullets). My next step is to investigate The QtScript module. Basically I want to be able to write the AI routines for the game in ECMAScript, so I can change them without having to recompile the game. This should also make the game easily extensible, possibly by people who aren't hard-core programmers.
Will post another video when I get something worth showing!