I think you are going to tell me to buy a new power supply right away. In my case, I've already got a 9700 Pro, that came with my Gateway 700XL, (rest of my specs in my profile). It has the stock power supply at 250 watts.
I'm thinking of getting a 800XT or 6800GT, kind of leaning toward the ATi. And I DO know these are power hungry cards, but my budget will be stretched with just getting the card, even without getting a new power supply, that's the reason for my question. I don't want to get a new card and then ruin it. But I might take a chance and get a new card, if I'm not taking a risk of doing any physical damage to anything in my PC.
Edit: I think that ATi said that the 9700 Pro needed a 300 watt power supply, but it has run fine on the 250 watt that Gateway so generously provided.