funny, because I was searching the same exact thing today. This is what I found, on an apple support forum (
http://discussions.apple.com/thread.jspa?messageID=8439074&tstart=0). FTA:
Do this.
1) Download the drivers for your version of the operating system at nvidia.com.
2) Run the installer. It will install the driver files in C:\NVIDIA, but the installer will fail saying it cannot find a compatible graphics card. That is expected.
3) Quit the installer.
4) Right click on your Desktop, go to Properties.
5) Click on "Settings " Tab at the top.
6) Click "Advanced" button,( it will be just abouve the "Apply" button.)
7) after that, click on the "Adapter" tab at the top, (the second tab)
8) Click Properties in the Adaptor Type section.
9) Click the Driver tab in th Properties window.
10) Click Update Driver.
after that, choose the radio button, No, not this time, click "next" after that.
choose "install from a list or specific location." radio button and click next.
select "Dont search, I will choose the driver to install" and click next.
13) Click the "Have Disk.." button.
14) Browse to "C:\NVIDIA\*winxp*\169.35\English". (*winxp* - this folder name might be different on yout computer.
15) Select nv_disp and click Open.
16) Now click OK.
17) Scroll down and select NVIDIA GeForce 8800 GTx.
18) Follow the rest of the prompts to install the driver. Windows will warn you that it cannot gaurantee that the driver you installed will work with the hardware, but I can because it works for
me.
19) Reboot your computer.
20) Your new card should now be working properly. You can even access the NVIDIA control panel!
Anyways, I will do this tomorrow, but give it a shot and let us know how it goes! I have actually read this before on another website as well. Also, just FYI, the iMac 8800GS isn't a mobile card at all. It is actually a desktop 8800GT underclocked to match the GS speed.