Turning off graphics card

[Til Schubbe]

Hello,

my computer is running 24/7. Normally there's nothing difficult to
do for the graphics card so the built-in motherboard-graphics card
is sufficient.

Sometimes I need some more graphics-power. In that case I'd like to
turn on the PCIe graphics card, run a 2nd x-server on it and some
power-consuming app (game) on that 2nd x-server. Finished with that
app I want to stop the 2nd x-server and turn off the PCIe graphics
card again.

Running the PCIe graphics card (e.g. Radeon 4670) all the time
would be a waste of energy and would make the fans run quicker and
louder.

Can I turn off (and on) a PCIe graphics card while the computer is
running?

If that's the wrong place to ask this, please point me to the
right direction (perhaps the kernel-ML?).

TIA
Til

PS: The computer is running Debian Lenny.