jquery vs ajax,jQuery vs MicrosoftAjax in ASP.NET MVC

Under what circumstances would you use MicrosoftAjax over jQuery in an ASP.NET MVC application?

According to Scott Cate in this podcast Object Oriented AJAX with Scott Cate MicrosoftAjax is good for sending and retrieving data to and from the server. And jQuery is good for manipulating your data via the DOM once it arrives at the client. Yet, with a simple form plugin for jQuery you can send and retrieve data with jQuery quite easily. Often with a single line of code.

So I'm wondering what the difference is between MicrosoftAjax and jQuery within ASP.NET MVC?