typedef enum _IRQ_DEVICE_POLICY
{
         IrqPolicyMachineDefault = 0,
         IrqPolicyAllCloseProcessors = 1,
         IrqPolicyOneCloseProcessor = 2,
         IrqPolicyAllProcessorsInMachine = 3,
         IrqPolicySpecifiedProcessors = 4,
         IrqPolicySpreadMessagesAcrossAllProcessors = 5
} IRQ_DEVICE_POLICY;

Windows Vista Kernel Structures