To enable intellisense completion for jQuery within VS you'll want to follow three steps:
Step 1: Install VS 2008 SP1
You can download VS 2008 SP1 here.
Step 2: Install VS 2008 Patch KB958502 to Support "-vsdoc.js" Intellisense Files
Step 3: Download the jQuery-vsdoc.js file
Save the jquery-vsdoc.js file next to your jquery.js file in your project (and make sure its naming prefix matches the jquery file name). For example, if the jQuery library file is jquery.1.2.6.js, the vsdoc file will be named jquery-.1.2.6-vsdoc.js
You can then reference the standard jquery file with an html <script/> element like so:
When you do this VS will now look for a -vsdoc.js file in the same directory as the script file you are referencing, and if found will use it for help and intellisense.