var randomlogo=new Array()

randomlogo[0]="0 -140px"
randomlogo[1]="0 -280px"
randomlogo[2]="0 -420px"
randomlogo[3]="0 -560px"

function changeLogo()
{
document.getElementById("logo").style.backgroundPosition=randomlogo[Math.floor(Math.random()* randomlogo.length)];
}

function changeLogoBack()
{
document.getElementById("logo").style.backgroundPosition="0 0px";
}