What you need to do is go into your display properties (Right click on desktop -> Properties) and go to the settings tab. If two monitors appear in the settings window, your computer is set up to support dual-monitors. Right click on Monitor Two, and select "Attached." Then check the box below that says "Extend my windows desktop onto this monitor." Chick apply, and you have two monitors! You may have to adjust resolution and color settings to get it just right.
There are a number of advatages to having dual monitors, including being able to have two programs up at once, much more desktop space, etc. The only real downside is that it takes more of your video cards processing time and memory, and takes up more room on your "real" desktop, but I personally love dual monitors. One for your business and the other to surf the web away!!
If you have any problems setting it up, consult the manual. (Or the products website if you've lost that) There may be something specific to your video card that I wouldn't know about.
Do let me know your thoughts on dual monitors.