There is nothing you can do about that. Starting with Windows Vista, Microsoft locked down the "interactable" sessions and so running WebDriver grid hub as a service which starts browsers in a desktop session will not work unless you are using Windows XP. So, what you need to do is have multiple grid nodes running in the foreground and leave those desktop sessions open in Windows 2008. Also, with Jenkins, running Selenium tests (without a grid) will exhibit the same problem where you'd have to run Jenkins in the foreground.
Windows says "By default, services use a noninteractive window station and cannot interact with the user. However, an interactive service can display a user interface and receive user input.". Also, "All services run in Terminal Services session 0. Therefore, if an interactive service displays a user interface, it is visible only to the user who connected to session 0. " See this site for this info.
The holy grail would be to write a Java program using SystemTray and then have the tray application auto-start a grid node session in the foreground when a desktop session starts. Just an idea since VisGrid cannot do this.
On Linux, there is a way to use xvfb to run grid as a service and run browsers in a headless session, but its a complex setup I think and I have never tried it. It's not very much different that the Windows situation anyway and I think the windows setup is easier.