function objfocused() {
    if (this.value == this.defaultValue) this.value = '';
}

function objblurred() {
    if (this.value == '') this.value = this.defaultValue;
}

function connectcallbacks() {
    var tags = document.getElementsByTagName("input");
    for (i=0; i < tags.length; i++) {
        if (tags[i].className.indexOf("field") >= 0) {
            tags[i].onfocus = objfocused;
            tags[i].onblur = objblurred;
        }
    }
}

window.onload = connectcallbacks;