I seem to remember, or not, a previous post of a similar nature and the solution was a setting in the bios relating to the Pci-e speeds, can't quite remember, I hate getting old
LOL
Perhaps you are thinking of the increase in PCI-e frequency upto 101..some Gigabyte boards respond to that, mine doesn't .
I have removed the 8800Gt and tried it in my old rig FX55 and Seasonic S12 (from 2005) the performance was astounding ...so it looks like the GT is working correctly, its either the Motherboard or the PSU, or something in Vista.
I am running the latest nvidia driver release [released Friday] and there is no more of the "card receiving insufficient power" Warning from the nVidia Sentinel, but it still won't run 3d06 benchie and the Vista experience index still crashes....and the grphics have a rating of 1.0