Window creation is window creation. You should be able to copy paste the thousands of working CreateWindow samples on the internet into a dll and run it.
Note that you don't *need* to use a windowproc on a custom window. There's a default which just noops all the messages (DefWindowProc). If you want a really simple create window sample,
http://www.winprog.org/tutorial/simple_window.html should work. Just replace WinMain with your dll entry. Remove the message loop, of course, and remove the WndProc function and just reference "DefWindowProc" as the function in your window class instead. If *that* doesn't work, nothing will.
It's best to start simple with these things. Adding your own logic before the you have the basics down is just going to confuse you. I'd suggest getting the above sample code working, and THEN add your own logic.
