function checkWindowSize(evt) {
    var width = 0;
    var height = 0;
    if( window.innerHeight ) {
        width = window.innerWidth;
        height = window.innerHeight;
    } else {
        width = document.body.clientWidth;
        height = document.body.clientHeight || document.documentElement.clientHeight;
    }
    if( height <= 700 || width <= 1024 ) {
        window.open('intro.html', '_blank', 'directories=no,toolbar=no, width=1024, height=768');
        Event.stop(evt);
        return false;
    } else {
        return true;
    }
}

var rules = {
    'a': function( element ) {
        Event.observe( element, 'click', checkWindowSize );
    }
};
Behaviour.register(rules);