video pop-up on LAN?

Easiest way I can think of, if you're not running a network DVR, would be to use an IP/network camera, plug it into the LAN, and just give everyone a web shortcut on their desktop that points to the camera (almost all of them have a built-in webserver to view the camera through).

since you allready have a camera installed,you should point to us what type of camera is there,is it a network cam? a web cam?or a standard security cam ?

if its any one of the first 2 choice,there is many solution and we need to know what cam it is to give you the good advice,if its a camera connected to a vcr or such setup, you should be looking at a analog to ethernet converter,most of those converter have a kind of web page that will be available by IE on a ip adress in your local network or even from the net

if you had an old camera and would like to change it,there is many choice,what i like a lot if network camera from panasonic,the nw1004 and nw244 both are good and even have audio built in..google on that..