msg_get_queue and resource IDs

Hi How can I find the IPC ID from a resource ID after calling msg_get_queue? I have a PHP script which communicates with some C applications via System V IPC messages. These applications reply back via a IPC channel number indicated within the request. The reply channel ID is generated via a "key" of zero to msg_get_queue (which equates to the kernel's IPC_PRIVATE). This is a recommended mechanism for bi-directional IPC comms. So essentially, is there a method of accessing the innards of a resource ID, or an alternative mechanism for calling the underlying msgget API? Kind regards Gary Partis