pagetitle = document.title;
loadeddata = 0;
alldata = 0;

function update(){
 ratio = loadeddata/alldata;
 window.setTimeout("update();",10);
 percentage = Math.round(ratio*100);
 if(ratio < 1){
  document.title = percentage+"%|"+pagetitle;
 }else{
  document.title = pagetitle;
 }
}

update();