To setup your MIDI device in Band-in-a-Box, go to Options | MIDI/Audio Driver Setup. And select your device as the input in this window.

Then to record, the button looks different depending on what layout you are in. In the classic layout there are separate buttons for recording MIDI and recording audio. In the modern layout, it's the same button and it opens a window where you can select which track to record to. If you are not recording audio at the same time, then set the audio track to none.

Attached Files (Click to download or enlarge) (Only available when you are logged in)
midi_record.png (37.5 KB, 75 downloads)
record_modern.png (14.09 KB, 75 downloads)

Best,
Chantelle