<SELECT id="select01" size="1" onchange="seltag()">
   <option value="1">1
   <option value="2">2
   <option value="3">3
</SELECT>

<script>
function seltag()
{
   var p;
   p=document.all["select01"].value;
  alert(p);
}
</script>

if (isset($_POST['u_name']))
{
    echo $_POST['u_name'] . '</p>';
}
 
else
{
    echo "<script type='text/javascript'>";
    echo "document.write('<form method=\'post\'>');";
    echo "document.write('<p>Ваше имя:
');";
    echo "document.write('<input type=\'text\' name=\'u_name\' value = \'' + userName3 + '\'</p>');";
    echo "document.write('<input type=\'submit\' />');";
    echo "document.write('</form>');";
    echo "</script>";
 
    exit();
}

<SELECT id="select01" size="1" onchange=<? echo $value ?>>
   <option value="1">1
   <option value="2">2
   <option value="3">3
</SELECT>
 

	<?php
	   $arr_book = array("1" => "Книга", "2" => "Учебник", "3" => "Брошюра"); //Тут массив				   
	   $arr_next = array("1" => "Самолеты", "2" => "Сделай сам", "3" => "Юнный техник"); 
	?>
	<form id="newFormAdv" action="#" method="post">
		<table>
			<tr><td><p>Выберите</p>
	<select name="book" onchange="document.getElementById('newFormAdv').submit()">
		<option value="0">Выберите книгу</option>												  
		<?php
		foreach($arr_book as $value => $book) {
		 $select = isset($_POST['book']) && $value == $_POST['book']?'selected>':'>';
		 echo '<option value="'.$value.'"'.$select.$book.'</option>';
		}
		?>					
	</select></td></tr>
	<?php if(isset($_POST['book']) && $_POST['book'] > 0) { ?>
			<tr><td><p>Выберите категорию</p>
		  <?php
			echo ($_POST['book']);
		?>
	</select></td></tr>
	<?php } ?>
		</table>
	</form>