This is not strictly a linux issue, but generic issue. I read in the manual that when installing PCIe x16, some jumpers need to be removed. Initially I did not do this, but the geforce worked none the less.
The manual says to remove JP92, JP88, JP91, JP83. However, when I do this, the jumpers fall apart: I end up with mainly the plastic body of the jumper, with most of the metalic bridges still in place, causing a mess on the motherboard.
After cleaning up, I noticed that it actually a sort of enable switch for the onboard DVI, and I suspect for the onboard HDTV as well.
 by Kennung Eins:
When I inserted my GF6200TC into the PCIe Slot, I also did not change the jumpers and everything worked. But I noticed (with the help of RivaTuner) that the videocard was running only in 32-bit mode (the memory interface, not the colors) while the card has a 128-bit memory interface. So I was wondering why it is only 32-bit and then I remembered the jumpers. When I removed the jumpers I again had a look in RivaTuner and now it recognized the 128-bit memory interface correctly. So probably the jumpers are not only for onboard DVI/HDTV but for the memory link to the northbridge as well.