CreateWindowEx with a custom control

I try to use the CreateWindowExA function with my own control (this just
displays a image and text), and it doesn't work.
I can use it with 'edit' or 'button' like:

IntPtr ptr = CreateWindowExA(0, "BUTTON", "", WS_CHILD | WS_VISIBLE,
1024, 4, 127, 23, m_pcoParent, IntPtr.Zero, IntPtr.Zero,
IntPtr.Zero);

I 've read, than for use this API with a custom control, I must use
RegisterClassExA.
I already tested, but that doesn't work!

can somebody help me?