intImage = 2;
function swapImage() {
var img = document.getElementById("IMG1")
switch (intImage) {

  case 1:  
   img.src = "http://mundolicious.com/ingejooris/afb/grasbanner.jpg"
   intImage = 2
   return(false);
case 2:
   img.src = "http://mundolicious.com/ingejooris/afb/grasbanner_tik.jpg"
   intImage = 1
   return(false);
 }
}

function roll_over(img_name, img_src)
   {
   document[img_name].src = img_src;
   }