[neurostep]

<input type="text" id="textBoard" value="" />
<input type="text" id="yadiv" value="" />
<script type="text/javascript">
var text = document.getElementById("textBoard");
var cloneText = document.getElementById("yadiv");
text.onkeyup = function() {
     cloneText.value = this.value;
}
</script>

все-таки value, а не innerHTML!=))
ASSWHOLE!!!