var norm = new Array();
var imgArray = new Array();
imgArray[0] = "mentor";
imgArray[1] = "master";
imgArray[2] = "custom";
imgArray[3] = "short";
imgArray[4] = "dip";
imgArray[5] = "intro02";
imgArray[6] = "intro03";


// Preload
if (document.images) {
  var over = new Array();
  var press = new Array();
  for(i=0; i< imgArray.length; i++) {
	if (i < 5) {
      over[i] = new Image();
      over[i].src = "img/courseNav_"+imgArray[i]+"_a.gif";
	} else {
	  over[i] = new Image();
      over[i].src = "img/course_"+imgArray[i]+"a.jpg";
	}
  }
}

function on(num) {
  if(document.images) {
    norm[num] = document.images[imgArray[num]].src;
    document.images[imgArray[num]].src = over[num].src;
  }
}

function off(num) {
  if(document.images) document.images[imgArray[num]].src = norm[num];
}