Andrew - sorry, I'm not following, do you already know what screen Orphus is using, and you have looked for an appropriate modeline? Or are you saying that this is unrelated to the screen? If the latter, what is this related to, as he seems just to be using a normal nVidia chipset with DVI output, plenty of people are doing that, surely, and not having this issue?
In the past, this seemed related to getting the porch timings right for a specific screen, and using a custom modeline to do so. But I seem to be missing something here, did I miss a thread related to this somewhere? Generally, you can solve overscan and displacement with the timing values, is this what you have confirmed doesn't work for his screen?