1998 Ford Taurus Timing Belt Wheel

One of the wheels on the timing belt stopped spinning or spins slowly. If the car starts quickly the belt will smoke.

Also the stuck wheel may be rusted, not sure. How serious of a problem do I have here?

Here's a youtube video of my timing belt, the red wheel sticks: Here's a youtube video of my timing belt, the red wheel sticks:

http://www.youtube.com/watch?v=fc2mdQoELuI