The information from this article applies to AGP-video cards although some principles (as well as BIOS parameters) are equally applicable to the old PCI-video cards.
So, how to increase an operating speed of video card? First of all, you can increase the frequency of system bus: the higher this frequency, the higher the speed of data exchange via a bus will be. Secondly, you can try to increase the performance of video memory or to speed up video processor. There are also the other ways for increasing the speed of video card. For example, you may install new drivers or reflash BIOS of your video card.
It should be noted that the overclocking of video system causes the heat increasing of video processor. That’s why before starting your experiments, ensure a good heat extraction. You may use the additional internal fans or replace the built-in fans of video card by more powerful ones. Some users recommend making experiments with overclocking outdoors at temperatures from +5°C to -5°C. Otherwise, closely monitor the changes of temperature range of your video processor during overclocking, especially while launching games. In case of significant temperature increasing, ensure the additional sources of cooling or reject overclocking at all. Remember, the temperature increasing decreases an operating resource of your video card and increases the risk of failures during its functioning.