macromedia flash sitedesign: Use a movieclip to do that..
If I understood correctly you want the mouse-over to happen only once,
right?
So create a movieclip with the button as you first want it to be seen
and on the second frame the way you want it after the mouse over.
The put simple actionscript to send the clips playhead to frame 2 on
mouseover.

on(rollOver){
this.gotoAndStop(2);
}

in earlier flash player versions it should be :

onClipEvent(mouseOver){
this.gotoAndStop(2);
}

Don't really remember at wich version the mc on() behaviour was introduced..

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