Is there a custom UserControl created in WPF that allows for RDP access. I know there's the ActiveX control for RDP 5.1 but I would prefer something that can be embedded within a Silverlight application.
You said both WPF and Silverlight? (they wouldn't be compatible more than likely).
There likely isn't one for WPF (as you said there's already an ActiveX control) and it would be extremely difficult to do for Silverlight, as there are a number of security restrictions on the use of sockets. For example, to use a custom socket, the target must listen on port 943 and respond with the Silverlight policy file. Secondly, Silverlight sockets are restricted to ports 4502-4534. So, you'd need to do some port redirection and additional work on the part of the target to even establish a connection. (Remote Desktop by default is set to 3389). Then, there's the actual challenge of implementing RDP in Silverlight (RDP being bitmap driven and Silverlight being vector based).