Yo lo haria asi:
Código PHP:
<?
$sql = "SELECT *
FROM videos v, users u
WHERE v.nick = u.nick
AND v.url = '$n'";
$result = mysql_query($sql);
while($row = mysql_fetch_array($result))
{
?>
<img src="<? echo $row['avatar']; ?>" width="80" height="80">
<?
}
?>