Best choice for IPC between service and user application on Vista / XP / 7

I hope this is the best choice of forum for this question-- I did a fair amount of searching a looking at forum names first.Our company has a client / server product running on XP which relies entirely on Windows messaging for IPC.  The app needs to send only short messages signifying state transistions and other info back and forth to multiple clients, one running in each user session.  The service is tied to hardware, and hence must run a single instance.We are now updating this app with Vista support, and I have just learned that session 0 isolation will break Windows messaging (different queues for session 0 and the user's).  My question for all of you in this forum is: which mode of IPC is the best way forward (RPC, named pipes, other), both for supporting Vi ...