Installing a video card is easy, its like insterting a nintendo 64 game, but a little harder. Also, you should know your power supply. Some cards have a requirments for power supply, a 8600gt requires 300-350 psu requirment I think.
Lastly, how much actually are you willing to spend on a graphic card? 8600gt is great if 50-80 is your limit. Just wondering, cause you can get a huge performance boost by spending 30-50 dollars more.