In Windows Vista, the new function (User Account Control (UAC)) is added to strengthen security. After setting UAC to valid, every operation requires the user’s permission.
* Please see this FAQ for more details - [Windows Vista] About user account control.
There are three different kinds of user accounts as below: Each account type gives the user a different level of control over the computer.
Administrator account can access all files on the computer and can carry out any change needed. In older versions of the Windows operating system, in order to change the configuration of the computer, it would be necessary to log on with an administrator account.
But in Windows Vista, if a Standard account or Guest account is used to log on, it is not required to log on with the administrator account due to UAC.
• Standard account
Compared with computer administrator, the account is forbidden from some management functions.
• Guest account
Provides an account to user who does not have a user account.
* Please see this FAQ for more details - [Windows Vista] About Guest Account