Changing the Account Used for Anonymous Authentication (IIS 6.0)
You can change the account that is used for Anonymous authentication in IIS Manager, either at the Web server service level or for individual virtual directories and files. You can also change the security settings for the IUSR_computername account in Windows by using the Group Policy Manager snap-in of the Microsoft Management Console (MMC). However, if the anonymous user account does not have permission to access a specific file or resource, your Web server will refuse to establish an anonymous connection for that resource. For more information, see Securing Sites with Web Site Permissions.
When you change the IUSR_computername account, the changes affect every anonymous HTTP request that a Web server processes. Use caution if you modify this account.
You must be a member of the Administrators group on the local computer to perform the following procedure or procedures. As a security best practice, log on to your computer by using an account that is not in the Administrators group, and then use the runas command to run IIS Manager as an administrator. At a command prompt, type runas /user:Administrative_AccountName "mmc %systemroot%\system32\inetsrv\iis.msc".
To change the account used for anonymous authentication