Sorak, I recommend you give freetrack a try (
www.free-track.net/english/)
I'm using it with a ps3 eye cam (got it used for $24) and works great.
I promise that once you get used to head tracking you will never go back!
If you don't want to modify a webcam or build a led array, you could also try facetracknior (
http://facetracknoir.sourceforge.net/home/default.htm) although I'm not still convinced about it.