$query = "SELECT * FROM firms WHERE firm_active='1' GROUP BY firm_name ORDER BY firm_name";
	$result = mysql_query($query) or die(mysql_error());
 
	print '<td><p>Предприятие: 
<SELECT name="user_firm" >';
	while ($row2 = mysql_fetch_array($result)) { print '<option value="'.$row2[user_firm].'">'.$row2[firm_name].'</option>'; }
	mysql_free_result($result);
	print ('</p></select></td>');

if($row["user_firm"] == $row2["firm_id"]) {
	print '<option value="'.$row2[firm_id].'" selected >'.$row2[firm_name].'</option>'; }
	else{	
	print '<option value="'.$row2[firm_id].'">'.$row2[firm_name].'</option>'; }
	} 

$qr_result = mysql_query("SELECT p.*, f.firm_name FROM projects p LEFT JOIN firms f ON f.firm_id = p.pr_firm WHERE p.pr_active = '1' LIMIT $start,$project_per_page") or die(mysql_error());
    echo '<table class="cool">';
	echo '<thead>';
	echo '<tr>';
	echo '<th>#</th>';
	echo '<th>Название проекта</th>';
	echo '<th>Предприятие заказчик</th>';
	echo '<th>Ответственный</th>';
	
	echo '<th></th><th></th>';
	echo '</tr>';
	echo '</thead>';
	echo '<tbody>';
	
	$i=1;
	while($data = mysql_fetch_array($qr_result)){ 

	$num=$start+$i;
	$i++;
	
//Дополнительный запрос
        $query2 = "SELECT * FROM users WHERE user_active='1' AND uid=".$data['pr_lid'];
	$result = mysql_query($query2) or die(mysql_error());
	mysql_free_result($result); 
	
		echo '<tr>';
		echo '<td>'. $num.'</td>';
		echo '<td><a href="/modules/projects/project.php?id=' .$data['pr_id']. '">'. $data['pr_name'] . '</a></td>';
		echo '<td><a href="/modules/firms/firm.php?id=' .$data['pr_firm']. '">' . $data['firm_name'] . '</a></td>';
		echo '<td><a href="/modules/users/user.php?id='.$data['pr_lid']. '">q'.$result['username']. '</a></td>';
echo "<pre>";
var_dump($result);
echo "</pre>";

projects (pr_id, pr_active, pr_firm(1), pr_user(2))
firms (firm_id(1), firm_name)
users (uid(2), username)

"SELECT p.*,u.username, f.firm_name FROM projects p LEFT JOIN firms f LEFT JOIN users u ON f.firm_id = p.pr_firm AND u.uid = p.pr_lid WHERE p.pr_active = '1' LIMIT $start,$project_per_page"

$qr_result = mysql_query("SELECT p.*,u.username, f.firm_name FROM projects p LEFT JOIN firms f ON f.firm_id = p.pr_firm LEFT JOIN users u ON u.uid = p.pr_lid WHERE p.pr_active = '1' LIMIT $start,$project_per_page") or die(mysql_error());

Таблицы:
projects (pr_id, pr_active, pr_firm(1), pr_user(2), pr_author(2))
firms (firm_id(1), firm_name)
users (uid(2), username)
--------

SELECT p.*,u.username, f.firm_name 
	FROM projects p 
		LEFT JOIN firms f ON f.firm_id = p.pr_firm
		LEFT JOIN users u ON u.uid = p.pr_user
	WHERE p.pr_active = '1' LIMIT $start,$project_per_page"

SELECT p.*,u.username, f.firm_name 
	FROM projects p 
		LEFT JOIN firms f ON f.firm_id = p.pr_firm
		LEFT JOIN users u ON u.uid = p.pr_user
		LEFT JOIN users u ON u.uid = p.pr_author
	WHERE p.pr_active = '1' LIMIT $start,$project_per_page"