I think my question isn't clear enough. Ok. Now I'll try to explain it much better. Main phrase is that:

"DXDraw1's Surface or any DirectDraw's Surface color depth is depended display bitcount." It means:

In fullscreen mode if we have a DXDraw1 component and when this DXDraw1 is initialized, DXDraw1.Surface's color depth or pixel format is the same with DXDraw1.Display.Bitcount.
In windowed mode If we have a DXDraw1 component and when it's initialized, DXDraw1.Surface's color depth or pixel format is the same with Windows system. (if Windows runs 32-bit, the surface is 32-bit.)

In my project, I need to specify the surface color depth without depended on display color depth or bit count. For example, display or screen color depth is 32-bit and DXDraw1.Surface or any DirectDraw's Surface color depth is 8-bit.

I'm working on it in two days and I'll be crazy. Please help me...