function imgSwap(tsImg, tsSrc){
  var objStr,obj;
	if(document.images){
    if (typeof(tsImg) == 'string') {
      objStr = 'document.' + tsImg;
      obj = eval(objStr);
      obj.src = tsSrc;
    } else if ((typeof(tsImg) == 'object') && tsImg && tsImg.src) {
      tsImg.src = tsSrc;
    }
  }
}

function preloadImages() {
  if (document.images) {
    if (typeof(document.WM) == 'undefined'){
      document.WM = new Object();
    }
    document.WM.loadedImages = new Array();
    var argLength = preloadImages.arguments.length;
    for(arg=0;arg<argLength;arg++) {
      document.WM.loadedImages[arg] = new Image();
      document.WM.loadedImages[arg].src = preloadImages.arguments[arg];
    }
  }
}

preloadImages('images/screenshots.jpg', 'images/screenshots_grey.jpg', 'images/links.jpg', 'images/links_grey.jpg');