Sure this is very possiable and a good idea if you ask me. Lets see how this can be done. :thinks:
In the ACP i can make an area where you add a user that you want to be notified of if he/she post. Adding that to the database will be very simple. But the PMing and emailing part will be a little harder. There should be a feature to send the Admin a PM, Email, or both.
You will prolly have to make a dummy user to be able to send the PM. I've never hacked the pm or email code before but there is a hack that does send automated PMs when you move threads, i can look at that and see how this can be done.
I'll look into this for ya, no promises though.