I'm trying to figure out how to trigger my jQuery function each time a option is selected in my multiple selectbox?

Here is what i got:
PHP Code:
<select id="newbtn" name="test" multiple="multiple"> 
<?
    $str 
'<b>This is a test!</b>Why doesnt this WORK!<div>Just testing...</div>';
    
    
$results preg_match_all('~<([^/][^>]*?)>~'$str$arr); 
    
$arr array_unique($arr[1]);
    
    foreach(
$arr as $arr1=>$value){
        echo 
'<option">'.htmlentities('<'.$value.'>').'</option>';
    }
?>
</select>

<?
echo '<div id="strDiv">';
echo 
$str;
echo 
'</div>';
?>
Code JavaScript:
$('#newbtn').click(function() {
	$('#strDiv').each(function() {
		var s = '<?=$str;?>',
		sel = document.getElementById("tags"),
		re;
		for (var i = 0, len = sel.options.length; i < len; i++) {
			if (sel.options[i].selected) {
				re = new RegExp(sel.options[i].text.replace("<", "<\\/?").replace(">", "[^>]*?>"), "gi");
				s = s.replace(re, "");
			}
		}
		$(this).html(s);
	});
});

Nothing happens when a option is selected? If I do it with a button like this:

<input type="button" value="Go Jquery" id="newbtn"/>

Then it works, but I would like to do it without the use of a button...

Thanks in advance ;-)