In a previous post about the AJAX Extensions, I detailed the copy commands to retrieve the DLLs from the GAC. Same thing, this time for the ASP.NET 3.5 Extensions. If you are demoing CTP material in a hosted environment, you will likely need these in your app's bin to avoid the inevitable configuration error.

copy "C:\WINDOWS\assembly\GAC_MSIL\System.Web.Extensions\3.6.0.0__31bf3856ad364e35" C:\dev\MMVCApp\bin
copy "C:\WINDOWS\assembly\GAC_MSIL\System.Web.Extensions.Design\3.6.0.0__31bf3856ad364e35" C:\dev\MMVCApp\bin