SysUtils.IsLeapYear();
DateUtils.IsInLeapYear();

  unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

uses DateUtils;

procedure TForm1.FormCreate(Sender: TObject);
var
  b: Boolean;
begin
  b := IsLeapYear(2009); //False
  b := IsLeapYear(2012); //True

  b := IsInLeapYear(StrToDateTime('2009-1-1')); //False
  b := IsInLeapYear(StrToDateTime('2012-1-1')); //True

//  ShowMessage(BoolToStr(b, True));
end;

end.