Hello,
The ID that you see in the users tab is used to differentiate between sessions that are logged onto your PC. This doesn't mean that it is a person logged on. Session 0 is reserved in Windows Vista for services and other vital funtions.
Some software will create users accounts on your computer to be used for maintenance and other functions. They would be assigned a 1,2,3,etc... if the software wasn't written to take advantage of session 0. When you log on, your desktop session is assigned a number also. That is the one you are seeing under the Users tab in Task Manager.
To see the session ID that processes are using