The type of video card you should get depends on what games you are playing. Also, your power supply will limit the the card you can get. Some of the more powerful modern cards need far more than 250W. I don't think you will void the warranty by opening the case and installing a new video card. That said, there are several cards to choose from.NVidia GeForce 9800 GTX
- Not extremely new, but reasonably priced with good performance.NVidia GeForce GTX 260
- Newer and more expensive. It only really has two or three specs that are higher than the 9800 GTX.Asus ATI Radeon HD 4870
- More powerful, specs wise, than the GTX 260 but is more expensive than it.Asus ATI Radeon HD 4870 X2
- ATI's top-of-the-line card. It is two normal HD 4870's combined into one card. It competes with NVidia's GTX 280 card and sometimes out performs it.
All these cards require a better PSU than you have, the 4870 X2 requires a minimum of 650 watts.