Airchair,
If you are attempting to replace the automatically generated guitar track, then the answer is no. Since Band In A Box has only one audio track (PC version, I'm not sure about the Mac version) you could mute the guitar track and record your own guitar track as audio, but that would leave you no place to record anything else.

Moving everything to a DAW or Audio Sequencer would allow you to record all the tracks you wished.

If you are looking to record the guitar as MIDI, then you will need the appropriate guitar/MIDI interface, and however you have that set up, you can record that to the Melody track. However, your output will have to be on a single MIDI channel, and will need to be the same MIDI channel as the Melody.

If you wish to record each string as an individual MIDI channel, that is possible, but not in Band In A Box.

Gary

I'm blessed watching God do what He does best. I've had a few rough years, and I'm still not back to where I want to be, but I'm on the way and things are looking far better now than what they were!