Even after adding the IntelliSense file for JQuery, you might still get an error as below,
"Error updating JScript IntelliSense: jquery-1.3-vsdoc.js: 'jQuery.support.htmlSerialize' is null or not an object @ 1416:4"
Atleast in my case the reason was, i was using a JQuery-UI library and it was due to a conflict between the JQuery and JQuery-UI library. The first workaround i did was create an empty file for the Jquery-UI library with the extension -vsdoc.js or you can create your own intelliSense file.
Hope this helps.