Yeah, it is easy. Just delete the thing.
First, move all personal documents from the home's of your users into OS9's Documents folder (on the root of your hard-disk). Or to be safe, just move the home's themselves.
Open the terminal and enter the following command
ls -la /
This will give you a complete listing of every file and folder on the root of your hard drive. Copy and paste the listing to a text app and print.
Boot into OS9. Delete all file/folders not relevant to OS9. Some may be locked so option-empty trash. You may need a program like resedit to make some visible.
Keep for certain:
Applications (Mac OS 9)
Desktop DB
Desktop DF
Desktop Folder
Documents
System Folder
Temporary Items
TheFindByContentFolder
TheVolumeSettingsFolder
Trash
I have to declare myself not responsible if your machine or data gets messed up due to my advice.
If anybody else has anyhting to add...