SQL Server 2005
Members of the sysadmin fixed server role can perform any activity in the server. By default, all members of the Windows BUILTIN\Administrators group, the local administrator's group, are members of the sysadmin fixed server role.
ConceptsPermissions of Fixed Server Roles
Other Resourcessp_helpsrvrole (Transact-SQL)
Security Considerations for Databases and Database Applications
Help and InformationGetting SQL Server 2005 Assistance