body control modules

Will a hypertech program the BCM or just the main engine control computer?
Also check this out...any thoughts if it's worthhile getting?

http://www.autotap.com/products.html

Also here's another intesting link

http://www.obdii.com/

The Hypertech actually slightly alters the programming code in the PCM (Powertrain Control Module). I think it bumps the timing, and shift points, but only at WOT. I had a hypertech and I didn't like it. For the money, it didn't seem worth it.