--- ---

You need to create your own class with an Alignment property:

    { ... }
      TMyEdit = Class(TEdit)
      private
        FAlignment: TAlignment;
        procedure SetAlignment(Value: TAlignment);
      protected
        procedure KeyPress(var Key: Char); override;
        procedure CreateParams(var Params: TCreateParams); override;
      published
        property Alignment: TAlignment read FAlignment write SetAlignment;
      end;

    procedure TMyEdit.CreateParams(var Params: TCreateParams);
    begin
      inherited CreateParams(Params);
      case Alignment of
        taLeftJustify:
          Params.Style := Params.Style or ES_LEFT and not ES_MULTILINE;
        taRightJustify:
          Params.Style := Params.Style or ES_RIGHT and not ES_MULTILINE;
        taCenter:
          Params.Style := Params.Style or ES_CENTER and not ES_MULTILINE;
      end;
    end;

    procedure TMyEdit.SetAlignment(Value: TAlignment);
    begin
      if FAlignment <> Value then
      begin
        FAlignment := Value;
        RecreateWnd;
      end;
    end;

Also see Tip #159 for an alternative approach.