Periodically, readers will need to access files off old computers that they have kept stashed away for years (I still have my PowerBook 150, and will probably never get rid of it). If you are one of these people and have protected your old Mac with OS 9's password protection, there may be a chance you have forgotten your log-in password and cannot access your system. As with OS X, in order to get around the password protection in OS 9 you will need a boot CD, in this case preferably one that's loads the classic Mac OS.
To reset your OS 9 password, insert your classic OS installation CD and restart the computer while holding down the "C" key. The system will launch and display the hard drive on the desktop as usual. Open the drive and go to the "System Folder," followed by the "Preferences" folder. From there, remove the preferences pertaining to keychain access and any keychains. After this, restart the system and it should not require a password to log in anymore.
While you can do this from the Terminal using an OS X DVD, this will only work on computers that support OS X and have DVD players. Additionally, it is much easier to use the classic Finder to navigate the file system and remove these files.
Another option is to just reinstall Mac OS 9, which will require you to first rename the current system folder to something like " Old System Folder" and then use the OS 9 installer to put a fresh system on the computer. After doing this you should be able to boot into the system and retrieve files, and also drag items from your old system folder to the new one, if needed.
If you do not need your old Mac, and are just interested in retrieving files, there are several ways to get files off the computer. The first is to get OS 9 to run and then burn files to CD if you have a burner, or also network your OS 9 computer and grab files that way. Optionally, if your old Mac has either FireWire or USB capability, you can try mounting an external hard drive when booted off the installer disk and copy files from the Mac's drive to the external one.
The other way is to use Target Disk mode (for computers with built-in FireWire) to mount your old Mac's hard drive on your new computer and copy files over (keep in mind that since this makes the drive fully accessible, this option can be used as an alternative to booting off the classic CD to remove the keychain preference files in OS 9). To do this, boot the computer while holding the "T" key down until the FireWire symbol displays on the screen, and then connect the computer to another one with a FireWire cable.
Lastly, you can place your old hard drive in an external ATA enclosure (some options available here) and attach it to your computer via USB or FireWire. This may be the only option for computers that do not support FireWire and that do not have a functional CD burner or networking capability.