I noticed brief article on the Macfixit forums mentioning that you can use OS X's System Disk utility (which runs on OS 9) as a means of running more than one OS 9 version on the same partition.
For example, you could keep a "Work" and a "Games" OS 9 system folder on the same hard drive, and use the System Disk to specify which to use at startup.
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Mac OS X Hints
http://hints.macworld.com/article.php?story=20001122091450954