Hello,

this is indeed a Videocard problem. I dont have a ATI, so i cant give u a really good Advise.

It is normal that OSX works without any Videocard select. OSX then works in VESA mode, but u cant change the Screen Resolution and Quartz Extrem is disable.

I figure that your 2600HD has another ID as the 2600HD, and/or another NVCAP. This is a bit complicate. Give me a few minutes,maybe i can find something usefull for u.

Yes i find something usefull.
First u should boot OSX in safe mode OR without any Videocard Driver, i recommend the last .
Click on the Apple in the upper left coner , select About this mac, More Information. Select the Menu Graphic/Display there u will find ur Device ID. ( NOT Vendor ID ). Write it down.

Now there a two ways. U can modifed the ATIradeonX2000.kext ( Advanced User only :P ) or download a Package Here Click ME. Chose the one with a matching Device ID.

Good luck!

Oh , and good advise : When ur card have Dual DVI, chose the one near to the Mainboard ( from behind the Left one )

Edit again : Ok i see u have Laptop....forget this Dual DVI crap ^^