In the It's a visual world... post I mentioned that the new graphics in AutoCAD 2007 will place greater demands on PC graphics. You can tune the machine by selectively removing some of the more demanding settings, shadows especially, but a better card means a better experience. Besides once you try the new display features you won’t want to loose them!
To help with the “which card” dilemma Autodesk are testing & certifying card/driver combinations for use with 2007. This database will available to view on-line or for download after release.
UPDATE 25–03–2006: It’s now on-line: http://www.autodesk.com/autocad-graphicscard