Olly v2 allows debbuggin child proceses.. dunno if it help in your case though

bunion

I hope you checked out codeproject as well. There is some great info (with sources of course) on api hooking. You'd need some adaptation for windows 7 and you would need to disable the antivirus as well. Some av's can catch api hooking.

use windbg, set ".childdbg 1"

You could try putting a breakpoint somewhere on the internals of OpenMutexA (for the child) and CreateMutexA for the father.

Also some tool you might like: http://www.mediafire.com/?p8xf39q81ppzx5n (source included)

Greetings

A few days have passed, I am eager to know if my suggestion help you, how about the result? Does the breakpoint get hit if we follow the steps above? -_-