As far as I know, two people can work on the same computer at the same time; only one user can actually have control of the computer at a time. However, I believe NetMeeting allows control to be quickly switched back and forth between persons.
I recently experienced NetMeeting for the first time. A friend got online with me and quided me through a session with it. During the session, he granted me control of his computer, during which time I saw his desktop on my monitor and I had control of his computer, not him. After a short time, I then released control back to him. This could go back and forth.