need some help with VideoPortGetBusData

HI all,
I am very new to this field of device driver
I am using windows 2000 ddk kit and developing this driver on windows
2000 only.

Please help me out in getting the base address of the adapter device.
I am using Matrox graphic chip G200.
i want to write a miniport driver for this chip.
If I look into device manager, it gives me information that this
device is on pci bus 1, device 0.

So to get the base address of this device I am using
VideoPortGetBusData, according to document it should return the length
of the data return.
So I am checking it.
If I use it as follows it allways returns 0.

PCI_COMMON_CONFIG PciData;
vpStatus = VideoPortGetBusData( hwDeviceExtension,
PCIConfiguration,
0,
&PciData,
0,
PCI_COMMON_HDR_LENGTH);

VideoDebugPrint((0,"\nvpStatus is 0x%x \n",vpStatus));

Please let me know were am I going wrong............


Also I have tried with be EisaConfiguration.
For EisaConfiguration it returns same 0......
vpStatus = VideoPortGetBusData( hwDeviceExtension,
EisaConfiguration,
0,
&EisaData,
0,
PCI_COMMON_HDR_LENGTH);
VideoDebugPrint((0,"\nvpStatus is 0x%x \n",vpStatus));


BUt for CMOS it returns 64.
It fills up the Pcidata buffer.........

vpStatus = VideoPortGetBusData( hwDeviceExtension,
Cmos,
0,
&PciData,
0,
PCI_COMMON_HDR_LENGTH);
VideoDebugPrint((0,"\nvpStatus is 0x%x \n",vpStatus));

I am not getting what exactlly it means..........
Any of information regarding this will be very helpfull for me to go
ahead..