Оформил: DeeCo
Автор: http://www.swissdelphicenter.ch

 {With SendInput API}

 // Example: Send text 
procedure TForm1.Button1Click(Sender: TObject);
 const
    Str: string = 'writing writing writing';
 var
   Inp: TInput;
   I: Integer;
 begin
   Edit1.SetFocus;

   for I := 1 to Length(Str) do
   begin
     // press 
    Inp.Itype := INPUT_KEYBOARD;
     Inp.ki.wVk := Ord(UpCase(Str[i]));
     Inp.ki.dwFlags := 0;
     SendInput(1, Inp, SizeOf(Inp));

     // release 
    Inp.Itype := INPUT_KEYBOARD;
     Inp.ki.wVk := Ord(UpCase(Str[i]));
     Inp.ki.dwFlags := KEYEVENTF_KEYUP;
     SendInput(1, Inp, SizeOf(Inp));

     Application.ProcessMessages;
     Sleep(80);
   end;
 end;

 // Example: Simulate Alt+Tab 
procedure SendAltTab;
 var
   KeyInputs: array of TInput;
   KeyInputCount: Integer;

   procedure KeybdInput(VKey: Byte; Flags: DWORD);
   begin
     Inc(KeyInputCount);
     SetLength(KeyInputs, KeyInputCount);
     KeyInputs[KeyInputCount - 1].Itype := INPUT_KEYBOARD;
     with  KeyInputs[KeyInputCount - 1].ki do
     begin
       wVk := VKey;
       wScan := MapVirtualKey(wVk, 0);
       dwFlags := KEYEVENTF_EXTENDEDKEY;
       dwFlags := Flags or dwFlags;
       time := 0;
       dwExtraInfo := 0;
     end;
   end;
 begin
   KeybdInput(VK_MENU, 0);                // Alt 
  KeybdInput(VK_TAB, 0);                 // Tab 
  KeybdInput(VK_TAB, KEYEVENTF_KEYUP);   // Tab 
  KeybdInput(VK_MENU, KEYEVENTF_KEYUP); // Alt 
  SendInput(KeyInputCount, KeyInputs[0], SizeOf(KeyInputs[0]));
 end;