When looking for a new video card for an older system there are a few things you're going to want to check:
- what graphics port does your motherboard have? (AGP, PCI, PCI-e)
- what power supply do you have? will it provide sufficient power? does it have enough of the proper type of connections?
- will the new video card fit in your old case? they make them big these days so you'll want to check, especially if you have a pre-built system like an HP or a Dell.