function checkValidNick(nick) {
	if(!nick.match(/^[a-z0-9_]{2,20}$/i)) return false;
/*	document.getElementById('nick-isok').innerHTML = ''; */
	var http_request=false;  
	if(window.XMLHttpRequest) { http_request = new XMLHttpRequest(); if(http_request.overrideMimeType) { http_request.overrideMimeType('text/xml'); } }
	else if(window.ActiveXObject) { try { http_request = new ActiveXObject("Msxml2.XMLHTTP"); } catch(e) { try { http_request = new ActiveXObject("Microsoft.XMLHTTP"); } catch(e) {} } }
	if(!http_request) { alert('Giving up :( Cannot create an XMLHTTP instance'); return false; }
	http_request.onreadystatechange = function() { 
		if(http_request.readyState == 4) {
			if(http_request.status == 200) {
				/* document.getElementById('nick-isok').innerHTML = ''; */
				if(http_request.responseText=='0') { 
					document.getElementById('nick-isok').style.display = 'none';
					return true; 
				} else if(http_request.responseText=='1') { 
					document.getElementById('nick-isok').style.display = 'block';
					document.getElementById('nick-isok').innerHTML = 'Ups, este nick ya existe! Por favor elige uno diferente!';
					return false; 
				} else { 
					alert('There was a problem with the request. I did not receive a boolean response: ' + http_request.responseText); 
				}
			} else { alert('There was a problem with the request. HTTP-Status is ' + http_request.status); }
		}
	};
	http_request.open('GET','/ajax/boolean-nick-exists.php?nick='+nick, true);
	http_request.send(null);
}