On PCs you could easily configure the Vertical Sync setting from NVidia control panel, how can you enable/disable vertical sync in OS X?
In OSX, Veritical Sync is called Beam Sync
Running the command
sudo defaults write /Library/Preferences/com.apple.windowserver Compositor -dict deferredUpdates 0 should do it for you, but you may need to reboot. Replace the 0 with 1 to re-enable.
You should also be able to do this by downloading this prefpane and looking under "System". Another way is to use Quartz Debug to disable it, but it seems like that has become harder to run on Lion & ML.