function cache_image ( imgName, src_on, src_off, width, height ) {
	eval ( imgName + "_on = new Image (" + width + ", "+ height + ");" );
	eval ( imgName + "_on.src = \"" + src_on + "\";" );
	eval ( imgName + "_off = new Image (" + width + ", "+ height + ");" );
	eval ( imgName + "_off.src = \"" + src_off + "\";" );
}
function button_on ( imgName ) {
	butOn = eval ( imgName + "_on.src" );
	document [imgName].src = butOn;
}
function button_off ( imgName ) {
	butOff = eval ( imgName + "_off.src" );
	document [imgName].src = butOff;
}