http://openmobile.svn.sourceforge.ne...92&view=markup you'll see how you can create a control by your self. Most of the normal graphic commands from .Net should be available for you to draw your control.
This could easily be quite an advanced topic, but do some digging on your side and look at the link I provided. This should at least get you started.
Yes communication to and from the application is hard but not impossible. To do some actual communication you could use windowsmessages to the application window but the results might be limited. Usually you're limited to what you would be able to do in the application by mouse or keyboard inputs.
If you look at this link then you'll see some info on the topic: http://www.codeproject.com/KB/miscct...rth_embed.aspx