Is it possible to set up OSX to go to log-in screen when inactive?

Okay, sort of relating to my Mail thread, but separate issue.

I only made the switch from Windows a year ago, so forgive me for being a bit thick.

I'd like to set up my computer to automatically require a log-in if I walk away from it for while. I know how to do this on windows, but I'm stumped on OSX.

I know this is possible, because I used to work in Apple in Cork (my introduction to the wonderful world of macology) and our workstations were set up to do so. I imagine it must be fairly simple, no?

Apps / utilities / keychain

If you go to edit, and change settings for keychain 'login', I think you can set it up there.

System Preferences - Security
About half way down is something like 'Require password to wake from sleep or screensaver' - put a check next to it.

This will require either putting your sytem to sleep or better, have a hot corner that auto starts your screensaver

Thanks guys.