Your thread made my computer crash! That hasn't happened, um, maybe ever before? I don't remember.
I think that any Mac from 2002 and earlier, and some eMacs and iBooks from 2003 are OS 9 bootable. Any Mac newer than that can't boot into OS 9, and can only run it in Classic.
To get you computer to boot in OS 9 (if it's old enough), go to System Prefs, Startup Disc, and select the OS 9 folder. However, that's what I did and my eMac crashed while it was loading what folders were available to choose from. My iBook, however (good old lappy) worked just fine. If you select the OS 9 folder and select restart, you're off to the world of old school mac world.