Is it possible to completely deactivate your gfx card while machine is idle, and let it reactivate when you start using the machine under win7. So that when it's idle there is no power consumption from the card?
If you go into sleep mode in Windows 7, the GPU turns off. That's as close as you can get for Nvidia I believe. AMD have the ZeroCore technology, which is more useful in crossfire configurations, but still useful for single gpu's, where the GPU turns off when the display is turned off. But yeah.
So basically, that's a no, it's not possible. gfx always has to be on, unless the vendor incorporated some sort of tech into the card, there is no windows feature that'll allow the cards to turn off when idle.
Well, when you say idle, do you mean display off or just like browsing the internet? On idle the GPU will be taking barely any power, and if it does turn off completely, you'll lose display to your monitor.