DirectX Overlay DLL

Hello, I am in need of a DLL that can be included in a C#, VB, VB.Net, or C++ Application. This DLL must be able to overlay a specific window's contents in a Full Screen DirectX Application. Sort of like how Xfire ([login to view URL]) 's chat client can be seen in a DirectX game. I would need the source code and the compiled binaries. ? ? I need? the DLL be accessable only by a certain application.. like: I build a new C# app. I call this DLL you would build for me. If this C# app is the the correct app the DLL was intended for the? DLL will work.. othewise not. so that if I destribute my application people cannot re-use my DLL.