Enabling Multiple Monitors
Your Hackintosh can benefit from the use of multiple monitors. Simply connect power to each additional monitor, connect a video cable from the back of the monitor to the video output jack on the rear of your video card, then power on the additional monitor(s). "Mirroring" in video terms means to duplicate (almost) everything from your primary monitor and duplicate the video on the additional monitor. Mirroring is practical if you're demonstrating actions to an audience and outputting said video to a projector of some sort. By default OS X will mirror the displays.
Go to System Preferences --> Displays, then click on the Arrangements tab. If you keep the lower left hand box of "Mirror Displays" checked, your monitors may look like this:
My desk usually doesn't look that clean, but I paid Industrial Light & Magic a handsome amount. The smaller monitor on the left is a Samsung 19" monitor from 2005 while the monitor on the right is my newer ASUS 28 widescreen monitor. While it may be hard to tell, the monitor on the left has empty space at the top and bottom because it is mirroring the main ASUS display which is widescreen. To change this I can click on the Display tab already in the Displays pane. There are two windows shown here, one for each monitor. The first selection in the list is "Optimize for:" with the "ASUS VN289" selected:
If I click this and select the Samsung monitor, then I get this:
I had to use a flash in this photo to emphasize the new difference. The Samsung monitor shows the desktop taking up all of the screen real estate, but now the ASUS monitor shows vertical black bars on the left and right sides because it has been optimized for the Samsung monitor.
Spanning the desktop is better used to take advantage of your desktop real estate. When you have more than one monitor, you can span the desktop to include your additional monitor for a wider, more productive experience. Simply return back to the Arrangement tab and uncheck "Mirror displays":
Now you can maximize your multiple monitor setup. You also have the ability to choose the main monitor where you Menu Bar and Dock appears (If the Dock is set at the bottom of the screen).
This screen allows you to click and drag items to better reflect the physical setup and change the main screen. The two blue screens in the screenshot above represent the two monitors connected to my Hackintosh. I can click and drag the thin, white menu bar from the monitor on the left (my smaller Samsung) to the larger blue monitor on the right (my ASUS widescreen), then my ASUS monitor will become the primary monitor. I can also click and drag the left monitor down a bit to better reflect the height difference between the two monitors. Alternatively, I can drag each blue square above on top of each other. If one of my monitors were physically stacked on top of the other, it would be practical to change this in the Displays preferences to better reflect the physical setup. Since they are side-by-side I can just leave this as-is.
The video card also enables the use of screen rotation. This feature allows you to rotate your screen orientation by 90˚, 180˚, or 270˚. If your hardware setup utilizes multiple monitors, screen rotation is independent from each of your monitors. In a dual monitor setup you can set one monitor in landscape mode and the other in portrait mode. If your setup utilizes a single widescreen monitor and you have a means to physically rotate it to a 90˚ angle, you can rotate it for a better elongated vertical view: