$(document).ready(function() {
    $(window).resize(position_wrapper);
    position_wrapper();
});

function position_wrapper() {
    var wrapper_height = $("#wrapper").height() + $("#footer").height();
    var window_height = $(window).height();
    var wrapper_margin = Math.max(8, (window_height / 2) - (wrapper_height / 2) - 20);
    $("#wrapper").css("margin-top", wrapper_margin+"px");
}