The AppointmentTooltip type is not some embedded in the dll type - it is actually the user control which is loaded in the tooltip. In order to use it you should have the same namespaces and you load it as you do with every standard user control you define yourself.
When you install RadControls, our online examples projects are automatically installed on your computer and you can not only examine their full source code, but also extend them further in order to meet your requirements.
You can open the demos from here:
Start\Programs\Telerik\RadControls for ASPNET AJAX\Open Sample WebSite In VisualStudio
The actual location on your hard disk is the following one:
C:\Program Files\Telerik\RadControls for ASPNET AJAX \Live Demos
I believe that examining the full source code will give you a better understanding on the demo scenario. In case you need further assistance, do not hesitate to contact us again.
All the best,
the Telerik team