This was addressed in a previous post on the Orbiter "official" forum recently I believe. Basically,
you have to make sure that:
1. You have the latest drivers for your card (I have a Ti-4200 128MB version, by the way)
2. You should install Orbiter again and make sure that the files all go into the correct folders.
3. In the Orbiter Launchpad, make sure that the video section settings are correct, especially the
3D Device setting (it should say something to the effect of "T & L" for your card.)
That should work. There's nothing wrong with the video card--it will handle Orbiter just fine.