Game Alpha testing

I’m currently working on a tile based game. I was wondering if anyone could help me tighten up the code, as far as hittests and the balls’ depth levels are concerned.
Also, I was curious about the difference between removeMovieClip() and detatchMovie()…if those aren’t the two commands I mean, you’ll have to excuse me-it’s late, and I should be going to bed instead of pleading for help on this game. All the same, I am curious about their different functions, and a better way for me to handle removing the ball movieclips from the screen once they hit a certain wall.
Well, that’s a mouthful, and any help at all is much appreciated. The code can be found here.

I may ask more specific questions in the days to come, but I figured I’d lay myself at the mercy of the community for a nice start.