//You need an anonymous function to wrap around your function to avoid conflict  
(function($) {

    //Attach this new method to jQuery  
    $.fn.extend({

        //This is where you write your plugin's name  
        setClickBlank: function() {

            //Iterate over the current set of matched elements  
            return this.each(function() {

                $(this).attr('orig', $(this).val());
                $(this).focus(
                    function() {
                        if (this.value == $(this).attr('orig')) {
                            this.value = "";
                        }
                        else if (this.value == "") {
                            this.value = $(this).attr('orig');
                        }
                    });
                $(this).blur(
                    function() {
                        if (this.value == "")
                            this.value = $(this).attr('orig');
                    });

            });
        }
    });

    //pass jQuery to the function,   
    //So that we will able to use any valid Javascript variable name   
    //to replace "$" SIGN. But, we'll stick to $ (I like dollar sign: ) )         
})(jQuery);