[Dim@]

TRos,
частая ошибка

<script>
function setOpacity() {
  var op = 0; 
  setTimeout(function (){
    if (op > 1) return;
    document.getElementById('big').style.opacity=op;
    op+=0.1
    setTimeout (arguments.callee, 100);
    }, 100);
}
</script>

<div id="big" onClick="setOpacity();" style="opacity:0.1">
blah-blah-blah...
</div>