Edit

Procedure TForm1.SendString(Text: String);
var
  PrevWindow: HWND;
Begin
  PrevWindow := GetActiveWindow;
  If Not(GetForegroundWindow = IChatHandle) Then
    Begin
      SetForegroundWindow(Hwd);
      PostMessage(Hwd, WM_SETFOCUS, 0, 0);
    End;
  SendMessage(Hwd, WM_SETTEXT, 0, LPARAM(PChar(Text)));
  keybd_event(13,0,KEYEVENTF_EXTENDEDKEY or KEYEVENTF_KEYUP,0);
  keybd_event(13,0,KEYEVENTF_EXTENDEDKEY,0);
  keybd_event(13,0,KEYEVENTF_EXTENDEDKEY or KEYEVENTF_KEYUP,0);
  SetForegroundWindow(PrevWindow);
End;

procedure TForm1.Button1Click(Sender: TObject);
begin
  SendMessage(Hwd, WM_KEYDOWN, VK_RETURN, 0);
  SendMessage(Hwd, WM_CHAR, VK_RETURN, 0);
  SendMessage(Hwd, WM_KEYUP, VK_RETURN, 0);
end;