From your question, it's obvious you have little/no experience working with computer hardware. Thus, I'd like to point out that graphics cards don't go into your monitor, they go inside your processor. (Don't be embarrased...we all start out somewhere, and the only way to learn is to ask questions.)
Given your "newbie" status, I'd highly recommend having someone else install the card for you, such as a geeky friend or the Geek Squad at Best Buy (though they'll charge you a "nominal fee"). Although the process is pretty short and easy, doing/touching the wrong thing could harm your computer and yourself.
If you post (or e-mail me) your model number I'll verfy that the graphics card will work on your computer. Also, if you would still like to install the graphics card yourself, I'll provide a link to step-by-step instructions on how to do it on your specific computer. (If you think you're up to it, it'll probably save you around $40.)
Hope this helps,
I've just recently bought a radeon 9200 atlantis graphics card. I'm using Compaq Deskpro and have all the system requirements, XP, enough memory etc. but I've failed at the first hurdle! I can't plug the card into the back of my monitor, there is nowhere for it to go. The cable from the monitor into the hardrive is secured into the back of the monitor, it doesn't come out. The only other cable is from the monitor to the mains. Do I need an adaptor or have I just wasted money?!