|"how do u know if u have a vidieo card or not"|
Look at the back of the computer case to see where the monitor cable connects. Have a look at the following pic...if the cable connects to the "C" area, you have onboard, if it connects to the "D" area, you have a video card. My guess is it connects to "C".
If you want to install a video card for gaming, you'll have to determine which upgrade slot you have available. It will either be standard PCI, AGP or PCI-Express. If you have an OEM sysytem (Dell, HP/Compaq, Gateway, etc), post the model number & one of us will be able to look up the specs & advise you what to get. Let us know how much you'd be willing to spend.