Help with simple comment form

[KDM]

Hi guys I'm trying to modify the following script so that only registered users can post comments.  Can you guys help please thanks?

<?php

require_once("admin_common.php");

session_start();

if(is_numeric($_REQUEST['id'])){
$imageid = $_REQUEST['id'];
}else{
header("Location: http://mysite.net/");
}

if($_POST['submit']){
if($_POST['username']==''){
	$err = "You must log in.";
}elseif($_POST['thecomment']==''){
	$err = "You have to enter a comment.";
}else{
	$name = strip_tags($_POST['thename']);	
	$themessage = strip_tags($_POST['thecomment']);	
	$ezdb->get_results("INSERT INTO user_comments (id,date_added, posted_by, message, image_id) VALUE ('','".time()."','".$name."','".$themessage."','".$imageid."')");
	$err = "Thank you for your comment.";
}	
}

if($err){
$err = '<span style="color:#FF0000;">'.$err.'</span>';
}

/* Update table `iid_ip`.

Between the dashed lines is the create statement used to create the image view count (iid_ip) table.

----------------------------------------
delimiter $$

CREATE TABLE `iid_ip` (
  `iid` int(11) unsigned NOT NULL COMMENT 'Image id from where the count is the number of unique views.',
  `ip` varchar(15) NOT NULL COMMENT 'The ip of the visitor.',
  PRIMARY KEY (`iid`),
  KEY `ip` (`ip`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COMMENT='Table for view count of image using unique ip''s.'$$
----------------------------------------

*/// Escape variables that are used in the query.
$_ip 	= mysql_real_escape_string($_SERVER['REMOTE_ADDR']);
$_iid = mysql_real_escape_string($imageid);

// Count is 0 if ip has NOT seen the images, else count is 1
$_count = $ezdb->get_var("SELECT COUNT(*) FROM `iid_ip` WHERE `iid`='$_iid' AND `ip`='$_ip'");
if (!$_count) {
// Insert the unique combination of image id and visitor ip in `iid_ip`.
// Method doesn't exists!	$ezdb->quick_insert('iid_ip', array('iid' => $_iid, 'ip' => $_ip));
$ezdb->get_results("INSERT INTO `iid_ip` (`iid`,`ip`) VALUES ('$_iid','$_ip')");
}
// Get count of image views.
$_views = $ezdb->get_var("SELECT COUNT(*) FROM `iid_ip` WHERE `iid`='$_iid'");
// And format, thousands seperator is a comma, no decimals.
$_views = number_format($_views, 0, '', ',');

/////////////////////////////

$page->addHTMLHead($scripthead);

$d[] = "<div id='imagedetails'>";

$imgs = $ezdb->get_results("Select * From image_map Where id='".$imageid."'");
$name = $ezdb->get_var("Select name From `".$imgs[0]->obj_type."s` WHERE id ='".$imgs[0]->obj_id."'");
if($imgs[0]->obj_type=='comment') $pg='comm';
if($imgs[0]->obj_type=='image') $pg='img';
$d[] = "<a href='imagepage.php?".$pg."=".$imgs[0]->obj_id."' style='text-decoration:none;'>«".ucfirst($imgs[0]->obj_type)."s - $name</a><br /><br />";
// DEFINE SIMPLE GRID
if ($imgs[0]->user_id != 0) { 
$theuser = $ezdb->get_var("SELECT username FROM users WHERE user_id='".$imgs[0]->user_id."'");
} else { 
$theuser = $imgs[0]->creator_name;
}
$d[]="<div style='float:left; width:450px; text-align:center;'>	
<a href='contact.php'><img src='assets/images/leftAdjpg'></a>
            <br />
	<div style='font-size:12px;  margin-top:30px; margin-left:5px;'>
	".'Html Code: Use for websites, blogs, profiles and myspace.<br /><input name="textfield3" type="text" class="imagedetails_links" id="textfield3" onclick="this.select();this.focus()" value="<a href="http://www.mysite.net/imagedetails.php?id='.$imageid.'"><img src="http://www.mysite.net/uploads/'.$imgs[0]->link.'" border="0" alt=" " /></a><br /><a href="http://www.mysite.net"></a>" size="70" /> <br />


	For posting in forums use this: <input name="textfield6" type="text" class="imagedetails_links" id="textfield6" onclick="this.select();this.focus()" value="[url=http://www.mysite.net][img=http://www.mysite.net/uploads/'.$imgs[0]->link.'][/url]" size="70" /> <br />
	</div>

	<div style="float:left; width:450px; margin-left:34px; margin-top:5px;"><table width="100" border="0">
  <tr>
    <td class="widgets"><a href="http://twitter.com/share" class="twitter-share-button" data-count="vertical">Tweet</a><script type="text/javascript" src="http://platform.twitter.com/widgets.js"></script></td>
    <td class="widgets"><iframe src="http://www.facebook.com/plugins/like.php?href=http%3A%2F%2Fmysite.net%2F&layout=box_count&show_faces=false&width=450&action=like&font=arial&colorscheme=light&height=65" scrolling="no" frameborder="0" style="border:none; overflow:hidden; width:450px; height:65px;" allowTransparency="true"></iframe></td>
  </tr>
</table></div>

	';



if(ereg('.gif',$imgs[0]->link)){
$thelarge ="<img src='uploads/".$imgs[0]->link."' alt='".$imgs[0]->name."' style='border:0px solid #cccccc;' />";
}else{
$thelarge ="<img src='imageresize.php?imagepath=uploads/".$imgs[0]->link."&width=500&height=500' alt='".$imgs[0]->name."' style='border:0px solid #cccccc;' />";
}

$d[]="
</div>
<div style='float:left; margin-left:10px;'>
	<p style='padding:0; margin:0; margin-right:20px; text-align:center; font-size:14px;'><a href='force.php?path=uploads/".$imgs[0]->link."'>Click to Download Image</a></p><br />
	".$thelarge."

	<div style='overflow:auto; clear:both'>
		<div style='float:left; text-align: left;'>
			Image: <span style='color:#FFFFFF;'>{$imgs[0]->name}</span><br />
			<span style='color:#ffffff; font-size:13px;'>Posted on: ".date('m-d-Y',$imgs[0]->date_added)." by ".ucfirst($theuser)."</span>
		</div>
		<div style='float:right'>
			<!-- Insert unique view count -->
			<span style='color:#ffffff; font-size:13px;'>Views: $_views</span>
		</div>
	</div>
".'
</div>

<div style="clear:both;"></div>
<div style="margin:0 auto;"><br />'.$err.'
	<form action="'.$_SERVER['PHP_SELF'].'" method="post" style="margin:0 auto; width:400px; color:#ffffff; font-size:11px; text-align:left;">
		<div style="margin-bottom:5px;">Leave a comment:</div><input type="hidden" name="id" value="'.$imageid.'" />
		Your name: <input type="text" name="thename" style="width:250px;" class="inputfields" value="'.$_SESSION['username'].'"/><br />
		Your comment:<br /><textarea name="thecomment" style="width:400px; height:70px;" cols="50" rows="4" class="textareas" ></textarea><br />
		<input type="submit" name="submit" value="Post Comment" style="float:right;"/>		
	</form>
</div>';

$getallcomments = $ezdb->get_results("SELECT * FROM user_comments WHERE image_id='".$imageid."' ORDER BY date_added DESC");
$uclist = '<div style="margin:0 auto; width:410px; padding:5px; border:0px solid #cccccc; margin-top:40px;">';
if(sizeof($getallcomments)>0){
foreach ($getallcomments as $ac){
	$uclist .='<div style="border-bottom:2px solid #333333; width:400px; color:#ffffff; font-size:12px; margin:0 auto; text-align:left;"><br />Posted on:<span style="color:#000000;"> '.date('m-d-Y',$ac->date_added).' at '.date('H:i a',$ac->date_added).'.</span><br />Posted by:<span style="color:#000000;"> '.strip_tags($ac->posted_by).'</span><br /><span style="color:#ffffff;">'.strip_tags($ac->message).'</span></div>';
}
}else{
$uclist.='<div style="border-bottom:2px solid #ffffff; width:400px; color:#ffffff; font-size:12px; margin:0 auto; text-align:center;">Be the first to leave a comment!</div>';
}
$uclist.="</div><div style='clear:both;'></div><br /><br />";

$d[] = $uclist."</div>";

$page->add($d);
echo $page->render();

?>