Took a while to figure out an easy way to install Classic after installing Panther on a new iMac:
- Use TinkerTool to switch on hidden files in Finder
- Insert the iMac Software Restore DVD
- Browse to the folder .images, then mount OS9General.dmg
- From the mounted disk image, copy System Folder (or Dossier Systeme, or whatever language it is) to your Startup Disk (Macintosh HD)
- Eject the mounted image
- Open the Classic pane in System Preferences, and make sure the new System Folder in Macintosh HD is selected. Tick 'Show Classic status in menu bar'.
- Start Classic, allowing you to run OS 9 applications.
An easier way would probably just be to boot from the Software Restore DVD and install Classic from there, if you don't mid restarting.