Setting up Dual Monitors

[boose_bagina]

I have a question regarding setting up Dual Monitors and I'd be extremely grateful if someone could help me out.

I'm looking into installing another monitor on the computer I currently use. I believe it has a built in video card, so I stole an ATI video card from my other cpu and hooked it in. Only problem is when I restart my computer, the video card I just installed is the only one my cpu recognizes and when I check in 'device manager', the driver for my original display adaptor is no longer there, and only the new adaptor is visible, thus I cannot hook up two monitors. I'm sure I'm just overlooking something and if someone could tell me what I'm doing wrong that would be awesome.

Thanks a bunch.