in the HEAD section:
<script type="text/javascipt">
function startDownload()
{
var url='http://server/folder/file.ext';
window.open(url,'Download');
}
</script>
in BODY
<script type="text/javascipt">
setTimeout("startDownload()",5000); //starts download after 5 seconds
</script>
or if you have just 1 download location you can combine the 2 in the body:
<script type="text/javascipt">
setTimeout("window.open('http://server/folder/file.ext','Download')",5000);
</script>
Edit: I wouldn't worry so much about the 0.01% that are paranoid and turn off javascript... But *do* provide a link in case a popup blocker kills the download.