Part of the tablet PC API is the Inkoverlay class. The constructor takes a control or even a windows handle. The user can scrible on the associated window. You can pass almost any handle to the constructor, like the handle of an ActiveX control on your Winform. This snippet makes the calender ActiveX a pen target:
private InkOverlay io;
io = new InkOverlay(axCalendar1.Handle);
io.AttachMode = InkOverlayAttachMode.InFront;
io.Enabled = true;
Now the user can scrible over the calender ActiveX control.
The control itself can no longer be clicked as it is shielded off by the ink-overlay.
There is one limitation to the handles accepted, they have to be owned by the same process. Passing a handle to (the mainform of) another application will result in an exception. Which is a pitty, else making a general annotation app for a tablet would have been very easy. It would be a matter of covering the app with an Inkoverlay object.
Peter