Why you should not run your computer as an administrator :
You should not add yourself to the Administrators group and you should avoid running your computer while logged on as an administrator. For most computer activity, log on as a member of the Users or Power Users group. If you need to perform an administrator-only task, log on as an administrator, perform the task, and then log off. As an example, create a user named goodperson. Assign a password and set this profile as a member of the users group with restrictions. Then log in as goodperson.
Running Windows 2000 as an administrator makes the system vulnerable to Trojan horses and other security risks. The simple act of visiting an Internet site can be extremely damaging to the system. An unfamiliar Internet site may have Trojan horse code that can be downloaded to the system and executed. If you are logged on with administrator privileges, a Trojan horse could do things like reformat your hard drive, delete all your files, create a new user account with administrative access, and so on.
You should add yourself to the Users or Power Users group. When you log on as a member of the Users group, you can perform routine tasks, including running programs and visiting Internet sites, without exposing your computer to unnecessary risk. As a member of the Power Users group, you can perform routine tasks and you can also install programs, add printers, and use most Control Panel items. If you need to perform administrative tasks, such as upgrading the operating system or configuring system parameters, then log off and log back on as an administrator.