What version of the SDK are you using? What versions of the dll's are you referencing? The Oct 2007 SDK was IIRC the last release containing the full MDX (samples, docs etc), the latest release contains the dll's but nothing else.
You should be referencing v1.0.2902.0 for Microsoft.DirectX and Microsoft.DirectX.Direct3D, the latest Microsoft.DirectX.Direct3DX is v1.0.2911.0.
You could try this (cobbled together, don't blame me if its wrong) code and just see what it comes back with:
try{ Format fmt = Manager.Adapters[0].CurrentDisplayMode.Format; if (!Manager.CheckDepthStencilMatch(0, DeviceType.Hardware, fmt, fmt, DepthFormat.D16)) MessageBox.Show("DepthFormat.D16 unsupported"); presentParams = new PresentParameters(); presentParams.Windowed = true; // Keep as discard, its the only valid SwapEffect if we use multisampling presentParams.SwapEffect = SwapEffect.Discard; // Do not wait for vsync, set to One or Default if vsync is required presentParams.PresentationInterval = PresentInterval.Immediate; presentParams.BackBufferWidth = this.ClientSize.Width; presentParams.BackBufferHeight = this.ClientSize.Height; presentParams.BackBufferCount = 1; presentParams.BackBufferFormat = Format.Unknown; presentParams.EnableAutoDepthStencil = true; presentParams.AutoDepthStencilFormat = DepthFormat.D16; device = new Device(0, DeviceType.Hardware, this, CreateFlags.SoftwareVertexProcessing, presentParams);}catch (Exception ex){ if (ex is DirectXException) MessageBox.Show((DirectXException) ex).ErrorString);}
The DirectXException will return the DX error code which you can then lookup in the unmanaged docs for the related method (in this case IDirect3D9::CreateDevice) - sometimes that helps trace the source of the error.
Pretty much the same code minus the depthstencil match works for me on integrated Intel 845 graphics hardware which is probably just as limited as your platform.
But as Mike says MDX is now unsupported so you might be better off looking at SlimDX or XNA where there is a lot more help available these days. I'll be jumping ship eventually when I can decide where to jump to...