If you just want to run classic mode, copy the System Folder from another Mac that has OS 9.1 (or better with 9.2.1 or 9.2.2) installed. A USB thumb dive works great for this. Transfer the folder to your Mac. It won't interfere with your OS X system which is in a folder titled System.
OS X 10.4.x Tiger is the last OS that supports running in classic mode.