First of all, check the FIDDLE DEMO
You can achieve this effect with a little JS work, in a cross browsers manner:
HTML
<input type="text" placeholder="Password" data-placeholder-note="(at least 4 characters)" />
JS (with jQuery)
$('input').each(function(){
var current = $(this);
var note = $('<span />').addClass('placeholder')
.text(current.data('placeholder-note'))
.insertAfter(this);
var origPH = current.attr('placeholder');
current
.focus(function(){
current.attr('placeholder', '');
note.hide();
}).blur(function(){
current.attr('placeholder', origPH);
note.show();
});
note.click(function(){current.focus();});
});
CSS
input {
position:relative;
font-size:18px;
width:220px;
padding:4px;
border-radius:4px;
}
span.placeholder {
font-size:12px;
position:relative;
left:-135px;
color:#bbb;
}