Ok, open the case, then unscrew the screw that is holding your old card in place. Just yank out the old card, and do with it what you will.
When you place the new card in, there is a slot on the case where a metal tab on your video card has to slide into. Place the card in, and make sure that all the pins are in the slots. Pushing it down may take some pressure, but I find that starting at the back and pressing gently down is the easiest.
Screw the card in, close your case, boot, and enjoy!
P.S. Did you uninstall all of your old drivers? That is an important step that may prevent future headaches.
<font face=tahoma color=red size=1>Knowledge is power.</font></td></table>