$(document).ready(function(){
  	$("#menu img.button").mouseover(function(){
		var currentState = this.src.indexOf("off");
		if(currentState){
			var newState = this.src.replace("/off", "/on");
			this.src = newState;
		}
		
	}).mouseout(function(){
		var newState = this.src.replace("/on", "/off");
		this.src = newState;
	})
	
});