Controlling Hardware Acceleration

I'm not sure what you mean exactly. When you create a D3D device with IDirect3D9::CreateDevice() you can specify D3DDEVTYPE_HAL for using whatever features that are supported by your hardware, or D3DDEVTYPE_REF to use a software emulation of all D3D features. The emulation supports all features but is slow since it does everything in software. Does this help you?

No i dont think so ...
I want to control or change the level of hardware acceleration that usually come by going to properties of VGA.

can we change or enable disable hardware accelaration?
I am using managed DirectX (direct3D).
acctually there are certian levels of hardware acceleration that means different at different level, i want to control this level or any thing with hardware acceleration.

Your questions or desires don't really make sense.

You control your graphics card through D3D or OpenGL and that is it.

Ok, you can disable the HW acceleration for D3D through the dx control panel or from your display properties. I don't see a reason to do this unless you are debugging your software.

The level of the hardware is something that you cannot modify, ie. if some graphics board does hardware acceleration, there is no way to really downgrade it, unless you write your custom driver or actually modify the board.

Perhaps you mean that you want to fix your software to work with certain level of hardware ? That is, that your software for example requires DX9 compliant GPU. There is no problem of creating a software vertex processing device with D3D and if that is what you want, then go for it.

Acctually i want to change this feature because my software is crashing after a long time running (8-9) hours.
this is happening on certain VGA cards (Radeon cards) which i think use come software with their drivers (Catalyst). this software also controlls Hardware acceleration or etc. by uninstalling this software we have come to know that system does not crash.

please can u help me on that all scenario.
thanx

If you've narrowed the problem to ATI's software, why don't you just contact them, explaining the situation and sending them a reproducible test case so that they can verify whether it's a bug in their software or yours?

(I do admit that the 8-9 hour running time that triggers the condition doesn't sound like easily reproducible.)

Usually, this kind of error is triggered due to some kind of overheating problems. The "extra software" wouldn't happen to be an overclocking utility, wouldn't it?