International keyboards are available in Mac OS X. This can be useful for typing in Spanish or French. This document describes how to make this feature available.
This is a per-person setting. Once set, it will follow that person from one computer to the next. This prevents problems like being unable to login because the keyboard is set to Spanish and you are unable to type your password.
If you followed steps under The Process above, you should now have a tiny flag in the menu bar on the right end. Using this, you can switch between keyboard layouts. You can also use the Keyboard Viewer to show where the letters are now placed on the keyboard.