How to manually install Classic Environment using a Mac OS 9.2.2 System Folder

I suggest that you grab the first download "Generic Classic Environment for Mac OS X 10.4 Tiger" here because it fits most needs, but feel free to try another Mac OS 9.2.2 System Folder if you want.  Download it on your Mac OS X 10.4 (or earlier) computer and expand the .sit archive.  Then drag the resulting System Folder to the Mac's hard drive. The standard location is at the top (root) level, but you can place it anywhere. If you downloaded a Classic Environment archive that contains an "Applications (OS9)" folder (optional) then also move that folder along.

Now, open System Preferences and click the Classic icon.  In the list, add the location of your Classic Environment folder and that's it.  Whenever you try to launch a Mac OS 9 or earlier app/game, it's gonna first launch the Classic Environment.  You can also make it so that when you boot your computer, Classic immediately starts loading.  It's up to you, but if you don't plan to use old Classic apps everyday, then don't do that, as it takes some time to load the Classic Environment and it consumes RAM once it's started.