9
All of the popular Javascript libraries have a "DOM loaded" event you can use for this.
Essentially:
<html>
<head>
<script>
// if using jQuery
$(document).ready(function() { $('#loading').hide(); });
// if using Prototype
document.observe("dom:loaded", function() { $('loading').hide(); });
</script>
</head>
<body>
<div id="loading">Loading...</div>
<!-- rest of page -->
</body>
</html>