Couldn't get HWSURFACE

Strangely, no matter how I tried, I couldn’t get a surface
from video memory using SDL_SetVideoMode(). I am using
Windows 2000 with nVidia Riva TNT2 32M mem, latest driver
from nVidia website and DirectX 8.0.

I tried testing programs from SDL-1.2.3, and there are
plenty resolutions available in full-screen mode, but I
just couldn’t get a surface from video mem :PP

What could be wrong?

Regards,
.paul.