typedef enum 
{
         PciExpressEndpoint = 0,
         PciExpressLegacyEndpoint = 1,
         PciExpressRootPort = 4,
         PciExpressUpstreamSwitchPort = 5,
         PciExpressDownstreamSwitchPort = 6,
         PciExpressToPciXBridge = 7,
         PciXToExpressBridge = 8,
         PciExpressRootComplexIntegratedEndpoint = 9,
         PciExpressRootComplexEventCollector = 10
} PCI_EXPRESS_DEVICE_TYPE;

Windows Vista Kernel Structures