I have Visual Studio 2008 Pro. SP1 and Hotfix
KB958502 – JScript Editor support for
“-vsdoc.js” IntelliSense doc. files
installed, but still no intellisense Support is available in VS2008.
<script type="text/javascript" src="Scripts/jquery-1.6.1.js">
$("#TextBox1").
</script>

You should use
jquery-1.4.1.js,jquery-1.4.1.min.jsandjquery-1.4.1-vsdocinsteated of version 1.6.1 in vs2008