codice:
<script type="text/javascript">
<!--
function swapF(from){
	var to,setF=false;
	if(from.type=='password'){
		to=from.form.holder;
	}
	else {
		to=from.form.pass;
		setF=true;
	}
	if(setF || from.value==''){
		// swappa solo se:
		// e' da settare il focus (quindi to e' pass)
		// oppure non viene inserito valore nel campo pass 
		to.style.display='block';
		from.style.display='none';
	}
	if(setF) to.focus();
}
//-->
</script>
codice:
<form>
<input type="text" name="holder" value="password" onfocus="swapF(this)" />
<input type="password" name="pass" style="display:none" onblur="swapF(this)" />
</form>
ciao