I updated the code below after talking to Ivan at WebKreator. It now works without opening a new window!
<body bgcolor="#FFFFFF" fgcolor="#000000" onload="javascript:endTime()">
<img src="" width=1 height=1 name="counter">
<script language="javascript">
<!--
var now = new Date();
var start = now.getTime();
function endTime()
{
var now = new Date();
var end = now.getTime();
timeToComplete = ( end - start ) / 1000;
alert( "this page took "+timeToComplete+" seconds to load!" );
document.counter.src="/icons/text.gif?time="+timeToComplete;
}
// -->
</script>