The Radeon 9200 workaround is unfortunately not very elegant, but as long as you copy everything from the disk image to your hard drive it ought to work.
A better workaround, if I may dare suggest, is to avoid running Celestia on the following hardware: Radeon 9000/9200, GeForce 4MX, GMA900. These are known to be crippled by serious hardware and/or driver bugs and limitations, and not just on the Mac.