Once you have the ASP.NET 3.5 Extensions CTP release installed, you can use VS 2008 or the free Visual Web Developer 2008 Express to create a new Web Site or Web Application Project that has the ASP.NET dynamic data support enabled:
The above walk-through only touches on a few of the scenarios and capabilities you can enable with ASP.NET Dynamic Data Projects.
If you're having issues installing Visual Studio 2008 RTM and had installed Visual Studio 2008 RC or if you want to remove it. You might want to consider using the following tool, which cleanly removes Visual Studio 2008 RC or RTM.
The ASP.NET AJAX Control Toolkit is a free download and contains more than 40 additional AJAX controls and components that work on top of the core ASP.NET AJAX functionality now built-into .NET 3.5 (and available as a separate download for ASP.NET 2.0).