var iPosition = 0
var sId = "Body"

function scrollBgUp(){
iPosition = iPosition + 1;
setBgPosition(iPosition);
setTimeout('scrollBgUp()', 1000)
}

function setBgPosition(iPos){
 oElement = document.getElementById(sId);
 oElement.style.backgroundPosition = "0px " + iPos + "px" 
}

iPosition = Math.floor(Math.random()*1000)
setBgPosition(iPosition);

//scrollBgUp();