I have had HEAPs of probs, you can see from my sig that I am back to XP. I keep trying Vista but no joy. I got it working with the old PD-SE but it would always loose the 5040 res after restart- too annoying, I have never managed to get the custom res working ever (they failed though it is working error) and because the NV drivers change so often, like another yesterday for Mirror's Edge (which I have), the effort you have to go through everytime is not worth it.
I had success on Vista 64 by rolling back to 178.13, setting up my resolutions, and then putting in the drivers I want. All the drivers after 178 caused that "custom resolution test failed" on success, but this one did not. Going forward, it seems to keep the resolutions on every update so far.
Of course, I'm not using a GTX 200 series, but I will be getting a GTX 295 soon, so I will post should I have problems. If you ever feel like trying again, that might help...