Oops, I think I meant to say they aren't jiggling back and forth. I slowed it down to 3 frames and it moves just like it should.
The background is black....but I like it that way. Hopefully that won't be a problem.
All of the buffer code should be correct. I won't go into details why I know that since it would be pretty long winded and pointless. However, it seems to me that the problem might be how long its taking the window to update. Say, when one frame is rendered, the next frame is rendered at such a speed that to the eye it looks like the last frame hasn't disappeared yet.
Don't know if this will help any, but this is a 'faked' picture of what it looks like. I used PrintScreen to take a picture of the game, but obviously it won't show the problem so I just copied and pasted the ball to show what it looks like when you play the game.