It is well known that no one should be running there computer logged in as an administrator. When you run as administrator you are running a risk of getting infected with something (virus [viri], spyware, others). When you run as a admin (Short for administrator) anything that can access your user-account has the same privileges as you (admin) so everyone should be using an account with lesser credentials.
XP Home: I know nothing works when you run as a limited user on XP Home and it is all but imposible not to run as admin except when using “SteadyState” a great program from Microsoft to edit user privileges and keeps your computer’s software in perfect working condition .
In Vista: After creating an admin account, login to “admin account”. Once logged in go to “Users Control Panel”, select “Admin” account and “Create Password”, select your user and switch Type to “Standard”.
When your in your standard user account and you do anything that will change the system it will prompt you for the password. You should think long and hard before putting in this password.
Windows XP Pro: This can be done in Windows XP Pro but it is much harder to configuer using GPE (Group Policy Editor). SteadyState is a much better choice for non-experts.