I don't think any card that uses under 300W in a machine will play CoD4....
and Max, if 125 fps is what Cod4 recommends, I'd like to see a monitor company that can make something run at 125 hertz, because thats the only way you would see the 125 fps take any effect. ie. you have a monitor that runs at 60hz, any fps higher than 60 will make no difference in the smoothness of the game. I think something above 30 is almost required for a twitch fps, something like mid 50's to low 60's, but a 125 standard is way too much. Maximum refresh rates for most CRT's are 85hz, and most LCD's are 75hz(depending on resolution and size).
Now as for this graphics problem, go for the Quadro FX 5600. lol j/k, I think you may be out of luck. But most 500watt power supplies are free after mail in rebates, check places like newegg.