First of all: You may already have OS9 on this machine. Booth the machine with the Option key held down and wait for a couple of minutes, you will eventually be given a screen with icons representing the valid OS's the machine can boot from. IF 9 is on the list, choos it and proceed.
Or, use the Startup Disk Preference Pane to select the OS you want it to boot.
If you don't have this option, Boot from the OS9 CD and choose install. It will install OS9 beside your OS 10.1