When you first install windows you'll be asked to enter a user name and choose a password. This will become the administrator account you'll use for all system-level changes, fixes, and updates. According to Microsoft it is better to create a standard user account for day to day use and reserve the administrator account for maintenance, backups, and system administration duties. it is good Idea because if you come into contact with a nasty piece of malware as a standard user in Vista or limited user in XP, it won't get very far in making too much damage to your system. Now go to
http://www.youtube.com/watch?v=v5-zmbx0qqg and watch a tutorial on how to set up user accounts in Vista. For setting up a limited user account in XP go to
http://www.youtube.com/watch?v=Jw4ZG8TPHaU. I hope you like the tutorials and awfully start using a standard or limited user account for safer computer experience.