There are two ways that you can start building applications with the Microsoft Ajax (Preview 6) release:

1) You can visit the ASP.NET CodePlex website and download the Preview 6 release (which also includes a large set of samples with it).

2) Alternatively, you can access the Microsoft Ajax Library scripts directly from the Microsoft Ajax Content Delivery Network (CDN).  You can do this by just adding the following script tag to either an .aspx or .html page:

<script src=”http://ajax.microsoft.com/ajax/beta/0910/Start.js”
      type=”text/javascript”></script>

You read my blog post from last month to learn more about the Microsoft AJAX CDN (or visit http://www.asp.net/ajax/cdn).