function ShortToLongFileName( FileName: string ): string;

var

  KernelHandle: THandle;

  FindData: TWin32FindData;

  Search: THandle;

  GetLongPathName: function( lpszShortPath: PChar; lpszLongPath: PChar;

                             cchBuffer: DWORD ): DWORD; stdcall;

begin

   KernelHandle := GetModuleHandle( 'KERNEL32' );

   if KernelHandle <> 0 then

      @GetLongPathName := GetProcAddress( KernelHandle, 'GetLongPathNameA' );

   // Использование GetLongPathName доступную в windows 98 и выше чтобы

   // избежать проблем доступа к путям UNC в системах NT/2K/XP

   if Assigned( GetLongPathName ) then

   begin

      SetLength( Result, MAX_PATH + 1 );

      SetLength( Result, GetLongPathName( PChar( FileName ), @Result[1], MAX_PATH ) );

   end

   else

   begin

      Result := '';

      while true do

      begin

         Search := Windows.FindFirstFile( PChar( FileName ), FindData );

         if Search = INVALID_HANDLE_VALUE then Break;

         Result := String( '\' ) + FindData.cFileName + Result;

         FileName := ExtractFileDir( FileName );

         Windows.FindClose( Search );

         if Length( FileName ) <= 2 then Break;

      end;

      Result := ExtractFileDrive( FileName ) + Result;

   end;

end;

procedure TForm1.Button1Click(Sender: TObject);

begin

   Caption := ShortToLongFileName( 'D:\PROGRA~1\' );

end;