|Look where the monitor cable connects. If it connects in the port area where the USB, sound, keyboard, mouse, network, etc are connected, you have onboard graphics. If it connects in the lower slot area, you have a card.|
If you're currently using the onboard & you want to upgrade to a card, you need to know two things:
1. which graphics upgrade slot you have available (standard PCI, AGP or PCI-express)
2. specs of your power supply, both the overall wattage & the amperage spec for the +12v rail
If the following applies to your system, it appears you only have standard PCI slots to work with:
What is the reason for this upgrade? Gaming? Post the games you're interested in. If you're stuck getting a standard PCI card, you're not gonna be able to play any recent games.