Windows uses a text file in the WINDOWS directory called WIN.INI to hold certain settings about the Windows environment, including a line instructing the computer what software to automatically run on startup. This line starts with the text 'run='. Any program after the equal sign automatically runs when Windows starts up.
The installer for the Color LaserWriter 12/600 PS restarts Windows in the middle of the software installation. It puts the text '_PPDSTRT' at the end of the 'run=' line so the installer continues once Windows is restarted. When _PPDSTRT is run, it brings up the 'Install PostScript Printer from PPD' screen.
Normally, the installer removes '_PPDSTRT' from the 'run=' line when installation is complete. However, if there is anything else on the 'run=' line when the software is installed, the installer will not remove '_PPDSTRT' from this line and the 'Install PostScript Printer from PPD' screen appears every time Windows is restarted.
To correct this, remove the text '_PPDSTRT' from the 'run=' line in your WIN.INI file.