What you may not realise, though, is that it is essentially the only way to protect your hard drive from mischief if you share your Mac. At Ease, Apple's now-defunct application for simplifying the Mac OS, no longer works under Mac OS 9 (installing Multiple Users causes At Ease to be trashed automatically, since they share many functions), and even the rudimentary protection provided by the Protect System Folder and Protect Applications Folder options in the general controls panel is no longer available. Open General Controls and you'll see what I mean - the options are tantalisingly still present, but irrevocably greyed out.
A voiceprint password essentially does what it sounds like it does: it allows users on your Mac to log in using a spoken password instead of a typed one. For this tutorial, I've presumed that you have not yet set up multiple user accounts. If you have, then you can skip ahead a bit. I've also presumed that you are the owner of your Mac, or at least the system administrator.
To use voiceprint passwords, you must have a PlainTalk compliant microphone. One of these should have come with your computer, and if not, your Mac reseller can help you out. Newer PowerBooks, iMacs and iBooks have such microphones built directly into them. You also need Apple Speech recognition version 2.01 or later. This will be on your Mac OS 9 CD.
The first thing you must do, before anything else, is open up the File Sharing control panel and ensure that an Owner Name and password are set up. The name and password you use in Multiple Users (not the voiceprint) should be the same as this. Then you can get started.
Note: Multiple Users replaces many of the higher-level security features of earlier versions of Mac OS, and thereby greatly simplifies the process of protecting your Mac. But it still leaves security holes big enough to drive a truck through. For instance, anyone with a Mac OS 9 CD can boot up from that and bypass Multiple Users altogether. For proper industrial-strength security, we'll have to wait for the beefier features of Mac OS X next year. However, Mac OS 9 also provides lower-level security such as file encryption through its under-utilised Keychain function. But that, as they say, is for another tutorial.