The bug in 3Dmark2000 is a bug in ddraw, we do not report 24/32 bit formats in a way the game likes. I have a patch for that deep down in my sending queue that fixes the depth and stencil masks.
This patch is still perfectly valid, just pointing out that in case of 3DMark2k it fixes the wrong bug. Other older apps are likely do demand D16, just 3Dmark2000 doesn't.