var sectorname = new Array('part1','part2','part3','part4','part5');

if (document.images) {
  var img = new Array();
  var imgOn = new Array();

  for(i=0; i< sectorname.length; i++) {
    img[i] = new Image();
    img[i].src = "img/"+sectorname[i]+".gif";
    imgOn[i] = new Image();
    imgOn[i].src = "img/"+sectorname[i]+"on.gif";
  }

}