yes that is possible, look in the manual under "Starting the Engine" for the comman dline option "-mon number" :
http://manual.3dgamestudio.net/"-mon number P A7.2
In a multi monitor systen, uses the monitor with the given number (1,2,3,...) for fullscreen display, instead of the primary monitor. For using several monitors at the same time, start the main application in server mode (-sv, see below) and start one client application per monitor (-cl -mon)."
But this isn't possible with only one instance as far as i know, you will need to open three instances (one for each monitor) and then let them communicate whith each other via, multiplayer commands !
