procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);

begin

 if ((UpCase(Key) < 'A') or (UpCase(Key) > 'Z')) then Key := #0;

end;

// Either disable the Beep in the OnKeyPress handler:
procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
 begin
  if key = #13 then // #13 = Return
 begin
  key := #0;
  // Code...
 end;
 end;
 // Or in the OnKeyDown-Handler:
procedure TForm1.Edit1KeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
 var
  Mgs: TMsg;
 begin
  if Key = VK_RETURN then
  PeekMessage(Mgs, 0, WM_CHAR, WM_CHAR, PM_REMOVE);
 end;