It depends on what your MIDI sound sources are, but all you need to do is set up an audio track(s) and record your sound souces while they are playing the MIDI data. In the case of outside keyboards/modules, send their audio signals to your line in on your sound card (a mixer comes in really handy here). In the case of internal sounds (ex. Soundfonts), set your soundcard's record mixer to record the MIDI source and then hit play. Either way, your sound sources playing the MIDI data will be recorded on the audio track. Quick and simple. Good luck!