<script type="text/javascript">
window.onload = function(){
    var links = document.getElementById('links').getElementsByTagName('a'), i = links.length, array = [];
    while(i--){
        links[i].onclick = function(i){
            return function(){
                if(array.join().search("#") == -1){
                    this.href = '#';
                    array.push('#');
                    return false;
                }
                else {
                    return true;
                }
            };
        }(i);
    }
};
</script>

<div id="links">
    <a href="http://ya.ru">link1</a>
    <a href="http://ya.ru">link2</a>
    <a href="http://ya.ru">link3</a>
<div>