interval = setInterval("switch_page()", 2500); 
$(document).ready(function() { 
    $('.link').mouseover(function () {
        var this_id = $(this).attr('id');
        var underscore_index = this_id.indexOf("_");
        var on = this_id.substring(underscore_index + 1, this_id.length);
        
        $('.page:not(#page_1)').hide();
        $('#page_'+on).show();
        clearInterval(interval);
        current = parseInt(on);
        $('.link').removeClass('link_on');
        $('#link_'+current).addClass('link_on');
    });
    
    $('#holder').mouseleave(function () {
        clearInterval(interval);
        interval = setInterval("switch_page()", 2500);
    });
});

var current = 0;
function switch_page() {
    if (current > 3) {
        current = 1;
        $('.page:not(#page_1)').fadeOut();
    } else {
        current++;
        $('#page_'+current).fadeIn();
    }
    $('.link').removeClass('link_on');
    $('#link_'+current).addClass('link_on');
}