I use this method of creating music for most of my halo machinimas, and as background music in my maps.
It's quite simple to learn, and if you have the cash, reason 4.0 is a great program for creating music.
Here is my tutorial for making a basic beat in Reason 4.0, you can use this method for doing things like scary background music or thrilling music in a single player level at a fighting area(just an example).
This is part 1:
http://www.youtube.com/watch?v=Wd6K-O9u_w4&hd=1This is part 2:
http://www.youtube.com/watch?v=C4fFGQkUwuo&hd=1If you want to skip into the tutorial and see what the final result can possibly sound like, watch part 2 first. If you don't like it at all, then there really isn't any reason to watch Part 1 unless you want to learn the software.
Have fun making songs for your maps!