To connect to a shared printer using Windows Vista or Windows Server 2008, the account you use must be a member of the local ...

To connect to a shared printer using Windows Vista or Windows Server 2008, the account you use must be a member of the local Administrators group unless the printer uses a printer driver package, a driver that is already installed on the local computer, or a driver that ships with Windows. Alternatively, you can disable this security prompt using Group Policy.