var inputs = document.getElementsByTagName("input");

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

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

for (i=0; i < inputs.length; i++) {
    if (inputs[i].className.indexOf("field") >= 0) {
        inputs[i].onfocus = inputfocused;
        inputs[i].onblur = inputblurred;
    }
}