вот накидал...
$res = mysql_query("select * from `lib` where `type` = 'bk' and `moder`='1' and `count`>'0' ORDER BY `count`");
$ccc = mysql_result($res, 0);
for ($i=0; $i <4; $i++)
{
$rand = rand(1,$ccc);
$arr = mysql_query("select * from `lib` where `id` = '".$rand."'");
echo '<b><a href="library/index.php?id=' . $arr['id'] . '">'.$arr['name'].'</a></b><br/>' . $arr['announce'] . '<br/>';
}