This is important: if you are shooting the actual show, don't use a flash. Ever. But try to avoid this by shooting the final dress rehearsal.
In general, theatre and dance photography is done with the show lighting, which has been created by a lighting designer for that show. Most venues actually have pretty good light on the stage -- those spotlights can be bright -- allowing handheld shooting at ISO 1600 or 3200 with f/2.8 lenses at reasonable shutter speeds (1/250 or better.) Sometimes they go for a dark and moody look, which wreaks havoc with still photography, like our recent production of Grapes of Wrath in which much of the show was shot at ISO 6400 at shutter speeds of 1/30 or worse. Got some good stuff, but had to work for it.
The D700 can provide excellent photos at high ISO settings. The very dark background and bright spotlights will fool your meter, causing your camera to overexpose, so shoot wide open, in manual mode, and check your photos and your histogram often, and adjust your settings as needed.
Good luck. Theatre and dance is fun to shoot but can be challenging.