Well it's hard to explain, but I'll try my best LOL XD.
1. Make sure you choose a new video card that is compatible with your computer
2. Uninstall the existing video card drivers. Right-click "My Computer," select "Properties," click "Hardware" and click "Device Manager." In the Display Adapter section, double-click your existing video card. In the Properties menu that appears, select the Driver tab and press the "Uninstall" button.
3. Unplug your computer power cord so you don't get a shock (you might want someone older/trusted to do this next part XD). Find the AGP slot on the motherboard of the computer once you open it up, and unscrew the old video card.
4. Put the new video card firmly in place, and install the new drivers.
Hope THAT helped, although it does seem very confusing XD. Your video card is the device that makes your screen and everything show up. If it begins to die, you will see lines on your screen like that, so I do believe yours needs replacing! LOL sorry for the confusion, and good luck X3