Código:
<html>
<head>
<title>Prueba login/password</title>
</head>
<body>
<form name="formLogin">
<table cellspacing="0" cellpadding="2" border="0">
<tr>
<td><input type="text" name="user" onblur="if(this.value=='') this.value='User';" onfocus="if(this.value=='User') this.value='';" value="User"/></td>
<td id="td_pass2"><input type="text" name="pass2" style="width:145" value="Password" onfocus="document.getElementById('td_pass2').style.display = 'none'; document.getElementById('td_pass').style.display = '';document.formLogin.pass.focus();"/></td>
<td id="td_pass" style="display:none"><input type="password" name="pass" style="width:145" onblur="if(this.value == '') {document.getElementById('td_pass').style.display = 'none'; document.getElementById('td_pass2').style.display = '';}"/></td>
</tr>
</table>
</form>
</body>
</html>
Espero que te sea útil !!