Interprocess communication in C without pipes or disk

A mate just called and was picking my brain about how best to handle inter-process communication in plain C.

His requirement is he has a monitor app watching a process and if that process goes dark he restarts it. However, sometimes that child app is actually still functioning - it's just a little busy and doesn't respond to the monitor's pings.

What he'd like is a way to have the child process increment a counter that the monitor can watch. If the counter is incrementing then it's all good and it'll back off. If the child goes dark and the counter stops incrementing then it's time to kick it.

Any thoughts on how best to accomplish this in the simplest, most member efficient way that doesn't require the installation of something like MSMQ?

Oh, and the kicker: it needs to support Windows XP and Windows 2003. There's a lot of those installs still out there...
cheers
Chris Maunder