Let's take a look at the final result we will be working towards.

Click a button rapidly to tell the Flash Player to repeatedly play a sound. You'll notice that the sounds produced by the left button overlap each other, where the sounds from the right button do not overlap. That is because a previous sound is stopped before a new one is played.

(Boing sound effect created by cfork, licensed under a Creative Commons Sampling Plus 1.0 License.)