function showPart(nr)
{
  var imgId = ["discPart01","discPart02","discPart03","discPart04","discPart05"];

  if((nr < 1) || (nr > imgId.length)) {
    alert("Error: Part-Id out of index!");
    return;
  }

  $(imgId[nr-1]).setStyle("visibility", "visible");

  for(var i = 0; i < imgId.length; i++) {
    if(i != (nr-1)) {
      $(imgId[i]).setStyle("visibility", "hidden");
    }
  }
}

window.addEvent('domready', function() {
  showPart(5);
});