Is there a way to run Growl as a Windows Service? I searched around SO, but have not found a solution, please let me know if there is one out there already.
Have you tried Microsoft's Srvany? Its pretty basic but should get the job done if your needs are the same.
This tutorial showing how to configure Growl with AlwaysUp should give you an idea of what to expect when running Growl as a Windows Service.