Change Channels on Your Set Top Box in Media Center with Free Programs

Via The Green Button:

Zapper (attached) is a free, open source, plug-in that will run any arbitrary command line when Media Center changes.

You might find it useful if your STB is not supported by the normal Media Center blaster, and you have some way of changing channels with the command line. (E.g. Girder and USBUIRT like me)

Or you can try another free program to control your set top box via the serial port: (may only work with certain set top box models):

I was able to spend some time and change DirectTVSerialControl to work with the motorola digital cable box. If you want to try it, at your own risk, extract the files in any folder and then run reg.bat to install it. A reboot is required. The config file is self-explanatory. To uninstall just run unreg.bat and reboot.
Enjoy, and let me know if it works or what issues are found.