$total = 0;
$sql = "SELECT COUNT( live_com.id ) AS nombre ".
       "FROM live_com ".
       "WHERE id_user = 1 ".
       "UNION ".
       "SELECT COUNT( news_com.id ) AS nombre ".
       "FROM news_com ".
       "WHERE user =1;";
//...
// code de connexion et d'exécution SQL
//...
$exec = mysql_query($sql);
while(false != ($n = mysql_fetch_assoc($exec)))
{
    $total += $n['nombre'];
}
/* Affichage de vérification */
$s = ($total > 0) ? "s" : null;
echo("<p>Total : ". $total ." message". $s ."</p>\n");

#1064 - You have an error in your SQL syntax. Check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT COUNT( news_com.id )
FROM news_com
WHERE user

#1064 - You have an error in your SQL syntax. Check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT COUNT( id )
FROM news_com
WHERE user =1 ) AS nombre
F

CREATE TABLE `live_com` (
  `id` int(6) NOT NULL auto_increment,
  `id_live` int(5) NOT NULL default '0',
  `id_user` int(8) NOT NULL default '0',
  `id_art` int(8) NOT NULL default '0',
  `art_type` tinyint(1) NOT NULL default '0',
  `texte` text NOT NULL,
  `date` int(10) NOT NULL default '0',
  PRIMARY KEY  (`id`)
) TYPE=MyISAM AUTO_INCREMENT=318 ;

-- 
-- Contenu de la table `live_com`
-- 

INSERT INTO `live_com` VALUES (6, 4, 1, 2, 1, 'Bon live !', 1161984492);
INSERT INTO `live_com` VALUES (7, 4, 1, 3, 1, 'ca aurait ete bien de le mettre ici carement si les orgas sont ok ... Quelques photos sinon?', 1161984532);
INSERT INTO `live_com` VALUES (8, 4, 844, 3, 1, 'Oui c'est UP !', 1161984972);
INSERT INTO `live_com` VALUES (13, 4, 1, 9, 1, 'Aie c'est grave la galere... les matchs doivent commencer quand ?', 1162025072);
INSERT INTO `live_com` VALUES (14, 4, 1, 7, 1, 'des choses qui arrivent ... :(', 1162025102);
INSERT INTO `live_com` VALUES (15, 4, -1, 10, 1, ':) :) des photos des photos ??? :)', 1162027088);
INSERT INTO `live_com` VALUES (16, 4, 844, 10, 1, 'ca arrive ;)', 1162027335);

CREATE TABLE `news_com` (
  `id` int(6) NOT NULL auto_increment,
  `date` int(10) NOT NULL default '0',
  `news` int(6) NOT NULL default '0',
  `user` int(6) NOT NULL default '0',
  `texte` text NOT NULL,
  PRIMARY KEY  (`id`)
) TYPE=MyISAM AUTO_INCREMENT=1279 ;

-- 
-- Contenu de la table `news_com`
-- 

INSERT INTO `news_com` VALUES (1, 1156983769, 264, 424, 'Wahouuu quelle est bien cette nouvelle version ! Avec tout ces lots de qualitay on devrait voir du monde arriver :D');
INSERT INTO `news_com` VALUES (2, 1156983963, 264, 1, 'J'espere bien ! :)');
INSERT INTO `news_com` VALUES (3, 1157006222, 264, 722, 'AHhhhhhhhhhhhh !!!!!! Bas là tout de suite on voit carrément mieux !! Bravo au designer !!\r\n\r\nPs: Ca va être carrément plus simple pour le concours de logo vu que l'on voit à quoi ressemble le site maintenant !!');
INSERT INTO `news_com` VALUES (4, 1157014576, 264, 668, 'hihi c'est joli :)');
INSERT INTO `news_com` VALUES (5, 1157015076, 264, 608, 'Pas mal, j'aime bien =)');
INSERT INTO `news_com` VALUES (6, 1157015142, 264, 1, 'Ouf, j'ai eu chaud ! :) merci :)');
INSERT INTO `news_com` VALUES (7, 1157016585, 264, 456, 'Bien Jouer Pirquessa et les autre pour cette news version ... :D BJ');
INSERT INTO `news_com` VALUES (9, 1157017254, 264, 1, 'Hum c'est tout de moi la :p sauf le design :)');
INSERT INTO `news_com` VALUES (10, 1157017452, 264, -1, 'Bien joué à tous ceux qui ont travaillé dessus :).\r\nvin100bk (htt://www.online-area.net)');
INSERT INTO `news_com` VALUES (11, 1157019531, 264, 112, 'j'avais bien dit que les commentaires serait bien à intégrer ;)');
INSERT INTO `news_com` VALUES (12, 1157019626, 264, 833, 'jolie design :)');

#1064 - You have an error in your SQL syntax. Check the manual that corresponds to your MySQL server version for the right syntax to use near 'ELECT count(id) as nombre FROM ( SELECT id FROM live_com WHERE

$sql = "
SELECT 
	date, 
	titre,
	url
FROM 
(
		SELECT 
			live_com.date, 
			CONCAT( CONCAT( CONCAT( CONCAT( 'live/', live.nom_url ) , '/news-LIRE-' ) , live_com.id_art ) , '.html#c0' ) AS url,
			live_news.titre as titre
		FROM live_com, live, live_news
		WHERE 
			live_com.id_user ='$id'
			AND live_com.art_type =1
			AND live.id = live_com.id_live
			AND live_news.id = live_com.id_art
		GROUP BY live_com.date
	UNION ALL
		SELECT 
			live_com.date, 
			CONCAT( CONCAT( CONCAT( CONCAT( 'live/', live.nom_url ) , '/interview-LIRE-' ) , live_com.id_art ) , '.html#c0' ) AS url,
			CONCAT( 'Interview: ', live_inter.titre)as titre
		FROM live_com, live, live_inter
		WHERE 
			live_com.id_user ='$id'
			AND live_com.art_type =2
			AND live.id = live_com.id_live
			AND live_inter.id = live_com.id_art
		GROUP BY live_com.date
	UNION ALL
		SELECT 
			news_com.date, 
			CONCAT( CONCAT( 'news-LIRE-0-', news_com.news ) , '.html#c0' ) AS url,
			news.titre
		FROM 
			news_com, 
			news
		WHERE 
			news_com.user = '$id'
			AND news.id = news_com.news 
		GROUP BY news_com.date
) AS d
ORDER BY date DESC
LIMIT 8";