Render an application (or the whole desktop) in directx

Hello. This will be my first post.

I'm looking for some help completing the following task. I've been learning directx b/c i'm going to change my current 2d windowed application to a 3d fullscreen. ITS NOT A GAME so i'm not going there. Its a front end for in car computer systems. www.mediaengine.org if you want to check it out. One of the things it does is launch applications using the createprocess api and then manages them and allows closing and showing focus, as well as embedding the application into my window (all so mediaengine can't lose focus, b/c that would be bad while in an automotive environment).
I've currently got a framework for directx that is fullscreen and just shows a moveable square. I want to render an application upon this square as if it represents the application when maximized on the desktop. I want to pass mouse events and kb events. (more about that later, i'm mainly interested in showing it. I'm not sure if the GetDC api in dx8 is what I need to look into.

I've written some pretty complex VB, but the directx is all new to me, so if you explain something, please be thorough on the Directx, but spare me the VB IDE stuff ;) Thanks so much