function PreloadImages(length, path, type) {
    for(var i = 1; i<=length; i++) {
        this[i]= new Image()
        this[i].src= path + i + type
    }
    return this
}

over=new PreloadImages(5,'images/over','.gif')
nav=new PreloadImages(5,'images/nav','.gif')

function rollOn(num){
if(document.images)
    eval('document.images["nav'+num+'"].src='+'over[num].src')
}
function rolloff(num){
if(document.images)
    eval('document.images["nav'+num+'"].src='
            +'nav[num].src')
}