Código PHP:
$currentPage = $_SERVER["PHP_SELF"];
$maxRows_rsPosts = 10;
$pageNum_rsPosts = 0;
if (isset($_GET['pageNum_rsPosts'])) {
$pageNum_rsPosts = $_GET['pageNum_rsPosts'];
}
$startRow_rsPosts = $pageNum_rsPosts * $maxRows_rsPosts;
$id_rubro = $_GET['idrubro'];
mysql_select_db($database_localhost, $localhost);
$query_rsPosts = " SELECT * FROM vposts";
$query_rsPosts .= " WHERE rubro1 = " . $id_rubro;
$query_rsPosts .= " OR rubro2 = " . $id_rubro;
$query_rsPosts .= " OR rubro3 = " . $id_rubro;
$query_limit_rsPosts = sprintf("%s LIMIT %d, %d", $query_rsPosts, $startRow_rsPosts, $maxRows_rsPosts);
$rsPosts = mysql_query($query_limit_rsPosts, $localhost) or die(mysql_error());
$row_rsPosts = mysql_fetch_assoc($rsPosts);
Muchas gracias!