Windows: Finding application that set environment variables

Is there a way on Windows to trace the changes from applications or scripts to environment variables on startup?

I changed an environment variable in the System->Advanced->Environment Variables dialog but its value is reset when I reboot my computer (I am an administrator on my machine). I'd like to track down the application that changes this variable.

Answer

I'm a n00b on Winders, but aren't environment variables always written to the registry? Possibly look for a registry monitor?