function swtch(num, imgname)
{
    if(document.images)
      document[imgname].src = img[num].src;
}

imgsrc = new Array();

imgsrc     [0] =  "img/header-links-1_off.gif",
imgsrc     [1] =  "img/header-links-1_on.gif",
imgsrc     [2] =  "img/header-links-2_off.gif",
imgsrc     [3] =  "img/header-links-2_on.gif",
imgsrc     [4] =  "img/header-links-3_off.gif",
imgsrc     [5] =  "img/header-links-3_on.gif"

if (document.images != null)
{
	img = new Array();
	for (i = 0; i < imgsrc.length; i++)
	{
	img[i] = new Image();
	img[i].src = imgsrc[i];
	}
}