function initialize_navigation() {

    var ultags = document.getElementById('main-nav').getElementsByTagName('ul')
    for (var i = 0; i < ultags.length; i++) {
        if (ultags[i].parentNode.parentNode.id == 'main-nav') { //first level
            ultags[i].style.top = ultags[i].parentNode.offsetHeight+'px'
        } else {
            ultags[i].style.left = ultags[i-1].getElementsByTagName('a')[0].offsetWidth+'px'
        }
        ultags[i].parentNode.onmouseover = function() {
            this.getElementsByTagName('ul')[0].style.visibility = 'visible'
        }
        ultags[i].parentNode.onmouseout = function() {
            this.getElementsByTagName('ul')[0].style.visibility = 'hidden'
        }
    }
}

document.observe("dom:loaded", initialize_navigation)