We have outlined the recommended approach for MOSS/Silverlight communication in our reply to your previous support ticket ("Reading Sharepoint List and Property Bag for Telerik Silverlight Chart"
) so we strongly believe WCF is the way to go.
If for some reason you do not want to use WCF, we would suggest you to check the official Microsoft Sharepoint Forums
for guidance as we believe this is a bit out of the scope of the Telerik RadControls suite (i.e. RadChart behaves as any other standard Silverlight databound control so if you are able to achieve the desired functionality for a ComboBox, you can use the same approach with RadChart as well).
Onto your second question -- you can either populate the chart manually, or use the built-in databinding infrastructure (more information can be found here
All the best,
the Telerik team
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