I noticed this is your first posting, hiimjamie3. Welcome to the Computer Forum!
Running two or more screens (some people like lots of video cards
can I get an "Amen, Reverend!" lol) is a feature on Windows that's called "extending the desktop" which basically allows you to extend your computer desktop view across multiple monitors. When I built my computer, I decided to get two 21.5" Asus HD 1080p monitors. My video card has two DVI (the video output cords with the white ends) ports so I was able to connect two monitors together. For example, I can watch TV (I have a TV tuner card peripheral) on Windows Media Center on one screen and play Call of Duty on the other.
When you set up to extend the desktop in the Screen Resolution window (right click menu on the desktop in Windows 7 and Vista), the computer can already detect multiple video outputs. By default, it only replicates the monitors (what is on one monitor shows up on the other). However, I simply have to select "extend the desktop" and I select which one is my primary monitor (the one that you want the taskbar to be on it, I use my left monitor by preference). After that, my two 1920x1080 resolution monitors virtually become one 3840x1080 resolution monitor. Your mouse is free to jump from one screen to the other; it's not bound to one screen. One keyboard will work just fine across both screens as well.
One of the neat things that you see on the Internet about having multiple desktops is utilizing all screens to play a game (Flight Simulator, Call of Duty, etc). That's a feature that I can utilize on Catalyst Control Center (the ATI graphics driver program) so essentially I can play COD on both monitors which is freaking awesome in my opinion. However, when you have the cross hairs set up in the middle of two screens, half of it sits on your left screen and the other is on your right screen. Of course, there is the physical edge of the monitors to contend with, so you're going to have some "dead space" between the two monitors that you physically see is there, but your monitor doesn't know the difference. Imagine it as warping through time, or using portal to jump across certain distances. It's also takes a little bit of practice to orientate yourself when you're lining up your 747 with the runway on it's final approach on FSX. lol
If you're worried about bogging down your system, just remember that if you are trying to run multiple things at the same time (Firefox, iTunes, Steam, Microsoft Office, etc) normally on one screen, it would not have an issue on the processing power. About the only thing that you have to worry about is the capability of your video card. I have an ATI Radeon 5830 (1GB GDDR5 256-bit) that works just fine with both monitors. Even when I have a full screen graphics-intensive game running across both monitors (the term HydraVision comes to mind for that feature, but idk if that's is the correct title) my computer performs alright. I recently purchased another ATI 5830 and CrossFired them (linked them together for better graphics computing power) and the picture is now amazing.
I'm pretty sure this is way more than you asked for but graphics are kind of my specialty. That, and I'm really good at crashing Windows (can I get another "Amen, Reverend!" from the Linux and Mac people? lol) Hope this has give you some insight on what can and cannot be done. If you need any more help we are here for you and always ready to lend some advice!
