What, you mean realistic physics? Get a physics textbook describing how pendulums swing. You should be able to figure out the X and Y coordinates from there...
Disclaimer: Any sarcasm in my posts will not be mentioned as that would ruin the purpose. It is assumed that the reader is intelligent enough to tell the difference between what is sarcasm and what is not.
Parabolas (or curves) that have a minimum value (open upward) have the general equation of: (x-h)^2 = p(y-k), where the vertex (lowest point in this case) is at the point (h,k), and p is a number greater than 0. So to find the y position at a given x-coordinate of the parabola: y= ((x-h)^2 / p) + k. You can go back and forth between a range of x values to acheive a swinging effect. You'll want the pendulum's speed to be inversely proportional to its horizontal distance from its center value. Fiddle around with the p term to achieve the arc you want. For the pendulum's bar, you might be able to use the DrawLine object. See, math is useful.
"Omg. Where did they get the idea to not use army guys? Are they taking drugs?" --Tim Schafer on originality in videogames