I have recently inherited a couple of applications that run as windows services, and I am having problems providing a gui (accessible from a context menu in system tray) wit
I want to echo mdb's comments here. Don't go this path. Your service is not supposed to have a UI... "No user interaction" is like the definining feature of a service.
If you need to configure your service, write another application that edits the same configuration that the service reads on startup. But make it a distinct tool -- when you want to start the service, you start the service. When you want to configure it, you run the configuration tool.
Now, if you need realtime monitoring of the service, then that's a little trickier (and certainly something I've wished for with services). Now you're talking about having to use interprocess communications and other headaches.
Worst of all, if you need user interaction, then you have a real disconnect here, because services don't interact with the user.
In your shoes I would step back and ask why does this need to be a service? And why does it need user interaction?
These two requirements are pretty incompatible, and that should raise alarms.