Multilevel buttons

Very new at Flash.

Using CS4.

I've managed to create some flash navigation buttons that are working just fine. Six buttons that fly in from the side and have "over" and "hit" properties all set up. But it's just a single level menu. I'd like to alter it so that when you hold the pointer over a button for 1/2 second or so (or if you click on it) a sub menu unrolls. I'm sure it's quite a bit more involved than the simple series of buttons I have so far but I can't find anything online that explains how to do this. Can anyone point me in the right direction?

TIA.