Exporting a wav w/ fixed start/end time (for looping background music)

I'm new at this too, but I guess the way I would do this is clone the track (assuming you'd like to keep the original intact), then remove all the other MIDI data except the part in the loop/trim off the excess space.  Once you have that done, you should be able to select that individual track and bounce/export it to audio without the rest of the song.
There is probably an easier way of doing this, but this method shouldn't really take all that long to do.
I suppose you wouldn't necessarily have to clone the track if you were exporting it outside of the project as you could just "undo" your changes provided that you resisted the urge to save until you had your project back to it's prior state.  I'm a little more cautious though so I'd probably clone the track just to be safe.