var addEvent = function(elem, type, fn) { 
    if (elem.addEventListener) elem.addEventListener(type, fn, false);
    else if (elem.attachEvent) elem.attachEvent('on' + type, fn);
},
textField = document.getElementById('nick'),
placeholder = 'Név';

addEvent(textField, 'focus', function() {
    if (this.value === placeholder) this.value = '';
});
addEvent(textField, 'blur', function() {
    if (this.value === '') this.value = placeholder;
});