I'm doing something similar in one of my apps. What I did was create two executibles. One for the app itself (MainApp), then another one that I want to run after the install ('RegisteredApp'). When you run the setup wizard on the 'MainApp' itself there is a place that asks you if you want anything to run after the install. That would be the 'RegisteredTo' app.
ICQ 10556 (ya), 254117