Script

(function($){
    $.fn.tabPanel = function(){
        var tabArea = $(this); // this == $(object)
        
        // eachメソッドを使って複数のjQueryオブジェクトに対しても処理を実行する
        tabArea.each(function(){
            var tabPanel = $('div.tabPanel',this); // eachメソッドの中ではthisが変わる
            var tab = $('ul.tab li',this);
            
            var tabSet = function(target){
                var targetTabId = $('a',target).attr('hash');
                
                tab.removeClass('active');
                tabPanel.hide();
                $(target).addClass('active');
                $(targetTabId).show();
            }
            
            tab.click(function(){
                tabSet(this);
                return false;
            }).each(function(){
                if($(this).hasClass('active')){
                    tabSet(this);
                }
            });
            
            if(tabPanel.filter(':visible').length!=1){
                tab.eq(0).addClass('active');
                tabPanel.not(':first').hide();
            }
        });
    }
})(jQuery);

jQuery(function($){
    $('div.tabArea').tabPanel();
});

Demo