imageName = new Array()
imageName[0] = "images/nav_about1.gif"
imageName[1] = "images/nav_about2.gif"
imageName[2] = "images/nav_affiliates1.gif"
imageName[3] = "images/nav_affiliates2.gif"

function swapOut(num,imgname){
     imgname.src = im[num].src
}
im = new Array()
for (var i = 0; i < imageName.length; i++){
       im[i] = new Image()
       im[i].src = imageName[i]
}