freeze button in down state?

instead of a button, you could use a MovieClip instance which contains two keyframes. One keyframe holds the up graphic and the second keyframe contains the down graphic. Using the instancename.onRelease and instancename.RollOut methods you could have the graphic toggle between frame 1 and 2 with instancename.gotoAndStop(2) and .gotoAndStop(1) respectively. Be sure to place a stop(); action in the action layer over each of the keyframes.

I don't think there is any way to freeze on the down state of a button. A possible alternative would be to have the button set the _visible property of a movie click that contians the down state of the button. The moive clip starts off with the _visible property set to false. On the mouse click, the property is set to true so it's visible. A mouse click on another button could set it to false again so it's invisble.