Set the input on Audacity to your soundcard (not sure what it'll be called), then hit record and play the drum track on Guitar Pro. Make sure the computer makes no other noise, or it'll be picked up.
Yeah, that's a way of doing it, but you'll still have the poor quality GP drums playing.

A better way, but more difficult, would be to get hold of Reaper. Reaper is another recording program, with a free demo and a $40 dollar licence at the end of it.

You can download a free drum plugin for some decent sounds ( blunoise mydrumset comes to mind ) and then export the MIDI into Reaper, assigning the drum plugin to the track with the MIDI data. Then you'll be able to record your guitar parts on top of this on another track.

That was a brief explanation, so if you require more detail just ask. The Audacity thing will work, but it won't sound as good, and if I'm not mistaken, not all soundcards allow you to select that setting on Audacity.
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