If you're like me you get tired very quickly, of waiting for the Startup disk Preference pane to load. A much faster method, is to use the Terminal command "bless" with which you can quickly and easily change your startup disk.
To change your startup disk to OS 9, type this in a terminal window:
sudo /usr/sbin/bless/ -folder9 '/Volumes/Mac OS 9/System Folder' -setOFNOTE: Replace "Mac OS 9" with the name of your Mac OS 9 partition.
sudo /usr/sbin/bless/ -folder '/System/Library/CoreServices' -setOFI put this into an AppleScript to make it even easier by calling a "do shell script" command. This sure has saved me a lot of time getting around the "Startup Disk Pref Pain". For more information regarding "bless" launch the "Terminal" and type "man bless" (without the quotes) for the "bless" manual pages.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020302215826526