procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
  if  (Key in ['0'..'9']) then
    Key := Chr(0);
end;

procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
  if (key in ['a'..'z','A'..'Z'])  then key := key
  else
    key := chr(0);
end;

procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
if not (key  in ['a'..'z','A'..'Z',#8,#126..#255])  then key := chr(0);
end;