What kind of 3D models? Pro-E ones? (yes, that is a guess from your name -- if you don't know what I'm talking about, then Pro-E, or Pro Engineer I think is its full name, is a 3D CAD tool)
There may be something Pro-E specific that doesn't work right with nVidia cards. Or, it is possible that you're seeing the same "slow performance" issue that a lot of people with GF2MX and GF4MX cards are seeing (though if so, this would be unique, because I think all the rest of these issues are with MX cards, not the GF2 Ultra).
Try running something like tuxracer, glxgears, or something like that. glxgears prints the framerate to the terminal you start it from every 5 seconds, and there's an option in the TuxRacer config file to turn on FPS reporting too. Post the FPS you get from one of these.