{ 
  Author  : Michael Puff - [url]http://www.michael-puff.de[/url] 
  Date    : 2006-03-01 
  License : PUBLIC DOMAIN 
}  

 
function ConvertStringSidToSid(StringSid: PWideChar; var Sid: PSID): Boolean; stdcall; external 'advapi32.dll' name
'ConvertStringSidToSidW';

 
function StrSIDToName(const StrSID: Widestring; var Name: string; var SIDType: DWORD): Boolean;
var
  SID : PSID;
  Buffer : PChar;
  NameLen, TempLen : Cardinal;
  err : Boolean;
begin
  SID = nil;
  err := ConvertStringSIDToSID(PWideChar(StrSID), SID);
  if err then
  begin
    NameLen := 0;
    TempLen := 0;
    LookupAccountSidA(nil, SID, nil, NameLen, nil, TempLen, SIDType);
    GetMem(Buffer, NameLen);
    try
      err := LookupAccountSidA(nil, SID, Buffer, NameLen, nil, TempLen, SIDType);
      if err then
        SetString(Name, Buffer, Namelen);
    finally
      FreeMem(Buffer);
    end;
  end;
  if Assigned(SID) then
    LocalFree(Cardinal(SID));
  result := err;
end;

 
procedure TForm1.Button1Click(Sender: TObject);
var
  Name : string;
  SIDType: DWORD;
begin
  if StrSIDToName('S-1-5-32-544', Name, SIDType) then
    ShowMessage(Name)
  else
    ShowMessage(SysErrorMessage(GetLastError));
end;