Codice da copiare fra i tag <BODY></BODY>

Ovviamente dovete sostituire "back.jpg" con il nome del vostro sfondo .

 

<script language="Javascript">

var background = "back.jpg"

var speed = 10;

browserName = navigator.appName;

browserVer = parseInt(navigator.appVersion);

if (browserName != "Netscape" || browserVer >= 4.5) {

function moveback(movert,movedn,hPos,vPos) {

  if (arguments[4])

    document.body.style.backgroundImage = "url(\"" + arguments[4] + "\")";

 

  if (arguments[5])

    document.body.style.backgroundRepeat = arguments[5]

  if (!isNaN(hPos)) {

    if ((movert!=0) && (hPos>0)) hPos=-100000

    hPos += movert

  }

  if (!isNaN(vPos)) {

    if ((movedn!=0) && (vPos>0)) vPos=-100000

    vPos+= movedn

  }

  document.body.style.backgroundPosition= hPos + " " + vPos

  if (isNaN(hPos))  hPos = "\"" + hPos + "\""

  if (isNaN(vPos)) vPos = "\"" + vPos + "\""

setTimeout("moveback("+movert+","+movedn+","+hPos+","+vPos+")",speed)

}

moveback(1,1,0,0, background);

}

</script>