Rollover Sounds in AS3

I have already received some good advice from theCodeBot on my last question so I decided I would try another. I am trying to get converted to Actionscript 3 from AS2. In old versions of flash, you simply placed the sound in a keyframe inside the button on the over or down state. Worked fine, but not anymore. I guess the sound must be set up with actionscript and a listener. I understand linkage. Is that the way to go? Can anyone give me a simple example of how to make one sound on the over state and a different one on the down state? Thanks.