attachRollOverEvent = function(imageId){
	$(imageId).mouseover( function(){ $(this).attr("src", $(this).attr("src").split('_off').join('_on')) } );
	$(imageId).mouseout( function(){ $(this).attr("src", $(this).attr("src").split('_on').join('_off')) } );
}


$().ready(function(){
	attachRollOverEvent("#nav_button1, #nav_button2, #nav_button3, #nav_button4, #nav_button5, #nav_button6, #nav_button7");
});