Maina Njuguna asked me what's required for a new desktop to run two monitors.
First, you need two monitors.
You'll also need a graphics card that supports two monitors. It's a pretty standard feature, these days. In fact, you'd probably have a hard time finding a new graphics card that doesn't. Even graphics integrated into a new motherboard will likely offer this support. You can easily check the back of your PC to see how many monitor connectors it has.
There are three different standards for monitor connectors these days--VGA, DVI, and HDMI:
You have to consider how many of each connector your graphics card provides before you buy the monitors. For instance, if your PC has one VGA connector and one DVI, you'll need a VGA monitor and a DVI one. Or you can buy an adapter--they're not expensive.
Windows 7 easily supports two monitors. To set it up, click Start, type screen resolution, and select Adjust screen resolution in the Control Panel section. The resulting dialog box will help you set up how the screens work together.
You might also want to check out Patrick Miller's video on the subject.
Note: This post was altered a few hours after it was posted. I made a really dumb mistake which you can read about in the comments below.