Hi,

To create something like you want I would use three windows. One for the top bar and two for the split screen.

The top bar is a transparent window which draws a bitmap with two widths. The lower part of the smaller area is transparent, too.
This window gets an always on top flag, since we want it to always overlap the right screen.

Now you can add some elements to the other windows (like buttons, text, etc.).

The upper part of the right screen is a bitmap, too.

Take a look into the attachement, there is an application what does something like you want (please excuse the look, I'm no designer..).

I hope this helps.

Regards,
Sven