Let me start with one problem I see in the markup you have provided. You will need a second Register
<%@ Register TagPrefix="telerik" Namespace="Telerik.Charting" Assembly="Telerik.Web.UI" %>
It is added automatically if you drag and drop the control onto the design surface in visual studio. You will also need to register the chart httphandler in the web.config file. The easiest way to do this is to use the control smart tag as shown here
In order to enable the design time for the control, you will need the Telerik.Web.Design assembly. It is installed in the GAC by the RadControls setup, but if you have used a .zip package you will need to add it to GAC or to the local Bin folder manually. You can find more details here
Finally, if these do not seem to help, please elaborate on the issue -- do you get any error message? What does it say if any?
the Telerik team