Do you have to use the recommended power supply for a video card?

I just got a ati 2900 xt card and it says it needs a power supply of 550. My current power supply is only 500. Thanks in advance.|||You could use a lower watt...but your performance is going to show the lack of power. I would go with AT LEAST the recommended power if not +50w|||If you have too many things drawing too much power (additional hard drives, optical drives, etc) from a power supply that cannot provide enough, your system may become unstable and crash randomly.