You can't reset an OS 9 password from a boot disk.
If you reboot into OS 9, just hold the shift key during boot to disable extensions.
If this does not work, you may be running some software usually used by schools to provide basically a driver-level login password. If this is the case, you will need to know the password, and unlikely to get around that.
Find an OS 9 installer CD, and boot to that. If you cannot boot (asks for a password) Then you may need to erase the drive
If you can boot to the OS 9 CD, then go into YOUR System Folder (not the folder named System, but the one named System Folder), open the Extensions folder, and take out the Multi-User Startup file. You should then be able to startup into OS 9.
If all you need is setting Startup Disk to OS X, so you can boot to OS X, you can do that while still booted to the OS 9 installer CD...
hope this helps