If you are a Blender pro, don't bother downloading this file. It is a simple setup to illustrate concepts such as tracking, parenting, object centers, IPO curves, constraints, particle systems, etc. Basically, my highly simplistic gun follows an Empty around the screen and shoots balls at it. Hooray! Still, I wish I would have found something like this when learning Blender. If interested, my tutorial on making this is here:

http://www.youtube.com/watch?v=NL-WWUkmfxk

Enjoy!