If you are using JQuery, you probably won't be getting any intellisense from Visual Studio 2008. But as part of ASP.NET MVC Microsoft started shipping JQuery. In order to make the Intellisense work follow the steps that i have tried,
1. Install the SP1 patch for your Visual Studio 2008. You can download the patch for free from here.
2. Download the install the patch that recognizes the -vsdoc.js intellisense files from here.
3. Download the vsdoc.js files from here and drop it along with your Jquery-x.x.js files.
4. To refresh the Intellisense from within our IDE you can use CTRL+SHIFT+J.
Hope this helps.