How to make AVI animation control really transparent?

Hi!

How can I make a AVI-animation control transparent? (Delphi 2.0, AVI in
seperate file, C/C++ should be similar)

I create it by the use of:

CreateWindowEx(0, (LPSTR(ANIMATE_CLASS)), nil,
   $50000000 or dwStyle, x, y, nWidth, nHeight,
    hwndP, 0, hinstance, nil);

I tried ACS_TRANSPARENT as dwStyle (where can I define the RGB-color to be
transparent ???) but the background is white then! (not the color window
grey it should)

are all parameters correct? (I ask because that's not documented
in Win32 Help)

Thanks in advance for your help!