Hi Steve,
Here is a link to the releases of the RadControls
http://www.telerik.com/products/aspnet-ajax/whats-new.aspx
Here is a link about Sitefinity's version
http://www.sitefinity.com/support/kb/sitefinity-3-x/how-to-check-your-current-sitefinity-version.aspx
http://www.sitefinity.com/devnet/forums/sitefinity-3-x/general-discussions.aspx
http://www.sitefinity.com/devnet/forums/sitefinity-4-x/general-discussions.aspx (Sitefinity 4.0 forum)
The controls written with Sitefinity's 3.x API cannot be plugged directly in Sitefinity 4.0. The API of Sitefinity 4.0 is different. The RadControls that we use are just a newer version.
Kind regards,
Ivan Dimitrov
the Telerik team