Heres another article on what vsync does....
Now, what is VSYNC? Well, VSYNC is basically the synchronizing of buffer swaps with your monitor's refresh rate. With VSYNC enabled, frame rates will not exceed the monitor's current refresh rate for that particular resolution. For example, if your monitor is using a refresh rate of 85Hz at 800x600, with VSYNC enabled, you will theoretically never exceed 85fps. So the refresh rate creates an artificial barrier that limits the frame rate.
So what happens if you are playing on an older monitor that only supports a 60Hz refresh rate. Will you have to live with a maximum of 60fps (assuming that your system can generate more fps)? Not necessarily. Newer video cards give you the option of disabling VSYNC. What happens is that this allows the buffer swapping to occur without synchronizing with the monitor's refresh rate. If it really was the refresh rate limiting you, disabling VSYNC may allow you to obtain frame rates in excess of 60fps. This, unfortunately, can also cause what are called 'visual anomalies': image tearing and flashing polygons. Some games run fine with VSYNC enabled, while other games crumble when VSYNC is disabled.
Read full article here...
http://www.d-silence.com/feature.php?id=255