The Windows Media Player ActiveX behaves differently than the normal Media Player.
Hardware Acceleration means that the video frames are not drawn by the CPU, but instead of the GPU. On newer systems the GPU also helps in decoding the video, but this feature requrires a DirectX 10 GPU and Windows Vista at least.
I'm not sure you can change this programatically, but you can look in the registry:
Make an export of the machine registry in regedit, toggle the setting, export again, diff the two files, now you got the setting, use the
Registry class's methoods to change the registry option if needed.