Once the MIDI drumset's MIDI output is connected properly to the computer's MIDi Input port and you have visited the MIDI Preferences selection section inside Powertracks and highlighted that MIDI interface on the Input side of the selection, all that you need do is to click on the track that you want to record to and hit the Record button. The tracks in Powertracks are already defaulted to MIDI tracks.

Playback may be another issue, though, if you are using a GM MIDI synth, the drumkit must be on channel 10 to access the Percussion sounds. Some few earlier synths may use channel 16 instead.

--Mac