$(function(){

    $("#nav ul li").hover(function(){
        $(this).addClass("hover");
        $('ul:first',this).css('visibility', 'visible');
    }, function(){
        $(this).removeClass("hover");
        $('ul:first',this).css('visibility', 'hidden');
    });
});

// preload hover images
var cache = [];

// arguments are image paths relative to the current page.
$.preLoadImages = function() {
    var args_len = arguments.length;
    for (var i = args_len; i--;) {
        var cacheImage = document.createElement('img');
        cacheImage.src = arguments[i];
        cache.push(cacheImage);
    }
}