How do you “take over” mac screens to show something on a network?

Bruce A.: How do you “take over” mac screens to show something on a network?
Say I’m in a computers class, and all the computers are connected through a network, and I figure out how to do something, and with the permission of the teacher I “take over” all the screens in the lab to demonstrate whatever this is. How is this accomplished?

Thanks, and clarity is appriciated

Answers and Views:

Answer by Adam
NetOP has a great program for PCs, and is slowly getting into the Mac field. Otherwise, I don’t know of any other off-the-shelf product that will do this. GoToMeeting.com supports Mac, but requires the end user to connect.