Windows Vista and Windows Server 2008 require that when multiple graphics adapters are used in a computer, they must be of the same display driver model type: either Windows Display Driver Model (WDDM), or Windows XP Display Driver Model (XPDM). If multiple WDDM graphics adapters are present, then they must all use the same WDDM driver. If the either requirement is not met, then Windows uses the adapter that was used to start the computer, and disables any others.
For more information, please see http://technet.microsoft.com/en-us/library/cc756392(WS.10).aspx. It applies to Windows Vista and Windows Server 2008, but I guess it's same with Windows 7 as Windows 7 also uses WDDM.
The system doesn't report Event ID 4103 as describe in the Technet link. However, as indicated before I configured the 82945g to use the same Standard VGA Graphics Adapter and was not able to resolve the issue.
Again dual display on different graphics chip is only supported on XPDM, which means you'll need to install XPDM driver for your BOTH graphics controller. For 82945G, you may try the Windows XP driver here: http://downloadcenter.intel.com/Detail_Desc.aspx?agr=Y&DwnldID=15618&ProdId=2102&lang=eng. I havent' tested it myself, but the idea is to install XPDM driver. Some more resources below: