Many of the sample ISV machines in your installation have Heidenhain postprocessors. I suggest you look at those, and choose one closest to what you want, and use it as a starting point in Post Builder.
For example, look at the in and mm versions in Program Files\Siemens\NX 10.0\MACH\resource\library\machine\installed_machi nes\sim01_mill_3ax\postprocessor\heidenhainTNC\