The AC compressor will not add a noticeable amount of drag to the engine as long as its turned off. The thing has a magnetic clutch on it and when the clutch is disengaged the pulley spins quite freely.

If you want to remove it to save a few pounds, now that's a different story. You may not be able to just go with a shorter belt because removal of the AC compressor might screw-up the belt routing for other accessories like power steering, the water pump, and the alternator. What you may need to do then is install a dummy pulley in place of the compressor to keep the belt pointed the right way. Check out Summit Racing. They carry a lot of kits like this that you might be able to adapt.