how to use overlay planes?

Hello everyone,

I’m looking for a solution to use overlay planes under Windows NT. I have a Nvida GeForce-3 graphics card with 64 MB of graphic memory.
I tried to figure out how to obtain an overlay plane as following but failed.

int i = DescribePixelFormat( hDC, 0, 0, NULL );
for( int j=1; j<i; j++)
    DescribePixelFormat( hDC, i, sizeof
          (PIXELFORMATDESCRIPTOR), &pfd1 );

    if( pfd1.bReserved > 0 )
        "I found overlay planes"
        "No overlay planes"

Whenever I runned the above, I always got 0 in the bReserved field. I think the GeForce-3 must have
at least one overlay plane, but it seems not.

If anybody knows how to obtain an overlay plane,
please tell me a detailed solution.