Hello Joe Weber,
Could you please check whether you have installed the Telerik.Web.Design.dll in Global Assembly Cache?
At this help article
you can find more details about deploying RadControls for ASP.NET AJAX in SharePoint.
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!