Hi Gary Blakely,
Since RadRichTextBox is current with CTP status it is not added to the toolbox automatically. We will add it in the upcomming beta version of our tools. Currently your option is to add it to your Xaml pages manually, as described here:
I hope this helps.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.