I beleive that you want dbcc_classguid = InterfaceClassGuid. Check out the example on MSDN.

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/devio/base/registering_for_device_notification.asp

Also in RegisterDeviceNotification the value DEVICE_NOTIFY_ALL_INTERFACE_CLASSES can be set and will ignore dbcc_classguid but that is only in specific cases.

xtx