Hi Forum. I am a newbie, but I'm learning a heck of a lot!

I have created a series of thumbnail buttons that load their full-sized images. Everything is working quite nicely, but at the moment, I don't know of a way to make the thumbnail button stay highlighted once it is clicked. I am using ActionScript and this is the code I use to make the thumbnail go from its 50% opacity (alpha) state to 100% (alpha) when the mouse rolls over, and then return to 50% when the mouse rolls out.

Code:
thumb01.onRollOver=function(){
	this._alpha=100;
}
thumb01.onRollOut=function(){
	this._alpha=50;
}
thumb02.onRollOver=function(){
	this._alpha=100;
}
thumb02.onRollOut=function(){
	this._alpha=50;
}
There must be a simple way to have the button remain at 100% opacity (alpha) once it has been clicked until another button is clicked. Could somebody help please?

Many thanks.