kmos: Removing OS X from an OS 9 system

To delete everything related to OS X, remove the following files and folders. Note that some files and folders listed as visible are invisible while booted into OS X, but are visible when booted into OS 9, and so are listed as visible here since I'm assuming a person removing OS X has already restarted directly into OS 9. Not all files or folders in this list may be present on your drive.

Visible Folders:

Applications
automount
dev
Library
Network
System (NOT "System Folder")
tmp
Users (see note below)
.vol

Open the System Folder, and remove the following files. While they are in the OS 9.x System Folder, they are only needed for OS X as Classic support.

Classic
Classic Support
Classic Support UI
ProxyApp

Visible Files:

etc
mach
mach.sym
mach_kernel
var

The mach files are normally visible when booted into OS 9.

Invisible Files:

.DS_Store
.hidden
.journal
.journalinfoblock
.VolumeIcons.icns

Invisible Folders:

bin
cores
Network Trash Folder
private
sbin
.Trashes
usr
Volumes

Some others that you may find that can be removed are:

lost+found (This contains iNode files recovered by the fsck facility).
.hot_files

Note: A word of caution. If you have done more with OS X than just play with it, then you have likely created files that you may want to save. Before deleting the folder Users, go through, in particular, the Music, Documents, Movies and Pictures folders of each user and either move to another location on the hard drive or external storage device, any files you don't want to lose. You can go through the other folders if you like, but you aren't as likely to find anything in them to keep, with the possible exception of fonts in the Users>user_name>Library>Fonts folder.

You can use File Buddy to track down all of these hidden files and folders and remove them. There will be lots of .DS_Store files. All that will be left on your hard drive after this are OS 9 and its applications.