How do I install a used Video Card without original installation disc with the drivers?

I bought the card used and it seems in good condition. I put it into my PCI slot (the right slot) after I downloaded the drivers to my desktop. I didn't disable the drivers to my onboard graphics card because I was afraid of what might happen if neither worked. What are the steps to installing a video card that I know is compatible with my computer? My computer is a HP pavilion a465c, with an onboard Intel Extreme Graphics 2 with 64mb of shared video memory. The Video Card I wish to install is a Visiontek 2600pro AGP 512mb. Please help, as I have so many games I want to play! The steps that work gets best answer!