Depending on what you want it to do, there are a variety of ways you could zoom a specific monitor.
To just have that monitor display things larger by default, you can set its resolution to something lower than it natively supports. i.e., if the monitor is 1920x1080, you could set it to 1280x720. This would have the effect that any window put on this monitor would appear larger than it should at the native resolution. Resolution changes on individual monitors are allowed in a multi-monitor system, so this would not affect your other screens.
Alternately, if you want the 3rd monitor to be the "zoom pane" for the other two primary monitors, you could use the Windows 7 Magnify tool. Magnify has a setting for a docked window which can be made to fill an entire screen. This way wherever you point the mouse on monitors 1 and 2 would show at a zoomed-in version on monitor 3. You would probably need a script or hotkey to keep this running between reboots, but it can stay up until deactivated.
1Can you better define "zoomed"? Are you talking about text/DPI scaling or screen magnification, or ??? Also, what have you attempted already and what were the results? – Ƭᴇcʜιᴇ007 – 2014-12-23T14:52:28.223
Jeez the Close Hammer is out already on this? Tough crowd. Probably screen magnification as I don't think the application window could be scaled. I haven't attempted anything as I don't have the monitor yet (holding off on purchasing until I do). – gravyface – 2014-12-23T14:58:39.650
If you don't know what you want exactly, then I'm not sure we can tell you how to achieve it. "Probably screen magnification" isn't much to go on. :) Good luck in your quest! – Ƭᴇcʜιᴇ007 – 2014-12-23T15:01:00.227
Well, it was more of a general question of whether Windows 7 can scale or zoom monitors independently. I'm not near a Win7 machine at the moment with dual monitors so can't really test it out. – gravyface – 2014-12-23T15:20:34.070