[рони]

yyyyuriyyyy,

а так?

window.onload = function () {
    var ratevalue = document.getElementById("ratevalue");
    var rate = document.getElementById("ratedisplay");
    var marks = document.getElementById("marks").getElementsByTagName("li");
    for (var i = 0; i < marks.length; i++) marks[i].onclick = function () {
        ratevalue.value = this.innerHTML;
        ratedisplay.className = "rate" + this.innerHTML
    }
};