There is a question; There is not one for the other way around. How do you change a username for a syd string, for example, to find out which HKEY_USERS subkey is related to a user of a given name? I tell the podcast that Ask, and answer, here goes. The easiest way is, on .NET 2.0 and above, this is: NTAccount f = new NTAccount ("user name"); Securityindifier s = (security identifier) f.Translate (typef (security identifier)); String sidString = s.ToString (); is the hard way, that when the work will not, and .NET 1.1 also works at: [DllImport ( "advapi32. dll ", charset = CharSet.Auto, SetLastError = true)] public static in exile bool LookupAccountName ([, MarshalAs (UnmanagedType.LPTStr)] string systemName, [, MarshalAs (UnmanagedType.LPTStr)] string account, IntPtr sid, Referee integer cbSid, stringbinder referenced denman name, referee int cbReferencedDomainName, use out); [DllImport ( "advapi32.dll", charset = CharSet.Au...