Um, hey there! First post and that. I just wanted to comment as I believe I know what it does so you can update your description.
This service lets Windows Vista detect other legacy services attempts to display a user interface or message in Session 0.
Many older third party services for Windows used to tried to display a message about their state to the user just by sending a message to Session 0's desktop which in Windows 2000 was the only session, and on Windows XP it was the default session (with additional log ons by users using Switch User going to Session 1 and 2 and so on).
In Windows Vista, to help isolate services from the desktop and harden the system against possibly security flaws, the first user is logged in to Session 1 and all services remain in 0. This means that any messages sent to 0 would be impossible to see!
As such, Vista will attempt to detect any activity in this session and display a message to the user, allowing them to switch user to that desktop so they can view the legacy message and dismiss it before flipping back to their regular scheduled programming. There is a
blog post here with a picture of that dialog and further links to these details.
Regarding turning it off, if you don't run any old pre-Vista third party system services on your machine, it should be safe to disable this service.
