Hardware Secrets published a guide about installing a second video monitor to your PC

With the prices of LCD monitors falling every day even regular users may be thinking of installing a second video monitor to their computer. With two displays you not only gain a bigger desktop, but you increase your productivity, as you can have two programs maximized to full screen at the same time (e.g. an Excel spreadsheet on one display and a Word document on the other display) and you won't waste time minimizing and maximizing windows to read and copy information as it occurs on a typical working environment with just a single video monitor. After working with two monitors it is hard to go back to a single display system! In this tutorial we will teach you how to check if your computer can accept a second monitor without any extra hardware parts, how to physically install a second monitor to your PC and all Windows configuration that may be needed. Read on.

How to Install a Second Video Monitor to Your PC