One of the things that I like about OSX is the multi-user feature. Windows XP supports multiple users however in order to ensure that everything runs ok, each users is typically set to Administrator. This is a very dangerous thing to do.
OSX on the other hand allows you to specify limited accounts for daily users. These Standard Users can do everything one would expect to do with a PC except damage!
Adding new users is accomplished through the System Preferences. This video will show you how to do it.
Make sure that you create separate accounts for each system user. This will give them their own environment to work in without fear that they will do damage to other users files. Your users will be happy and you will be happy not having to worry that you’ll be called in to fix system problems.