Locking the Screen on Mac OS X 10.6

I'm often asked by teachers, IT folks and mac switchers "How can the screen be locked on a mac?"

Cautious Windows users are used to pressing ctrl-alt-delete to be presented with a menu and a choice to lock the screen. Getting control of your computer back is as simple as entering your account password and you're off.
Such a feature does exist on the mac but it's hidden away a bit. Here is how you turn it on.
Open Keychain Access, it is in your Utilities folder which is in your Applications folder...
path to keychain access
Keychain Access is the application which looks after your Keychains! Keychains are used by the system to store private information like website passwords or passwords for services. Keychains are the files that store the passwords when you click that little "Remember my password" check box you sometimes see. 
From the Keychain Access menu choose Preferences... or press cmd-,
In the Preferences window that appears tick the checkbox labelled "Show Status in Menu Bar"
Keychain Access Preferences window
keychain menu iconIn the top right corner of your screen, along with the clock a new icon will appear looking like an open padlock. The open padlock shows that your login keychain is unlocked (the login keychain is the one storing your passwords)

enter your password dialog

Click on this padlock and you'll see some options the top one being Lock Screen. Choose this and your screen will turn black... it's locked!!
At this stage I should point out that once locked you'll need your password to unlock, so I hope you can remember it.
Just wobble your mouse or press a key and you'll get the enter your password dialog box. Type your password in and click OK, you'll be back to the computer as it was before you locked it.
That's really all there is to it, but some users may want to automate this process a little.
You could choose to activate screen locking after a few minutes or when you wake your computer from sleep. The option to do this is in the Security System Preference.
require password screen grab
So there you go. Just a couple of ways you can make your mac a little more secure.