PHP upload script

[jacob21]

Hi,
I am uploading a file & sending uploaded file to mail id. its working fine.I want to add validation in it.
when there is no uploading of file.it shows error i.e mail sending failed due to unattached document.

My code is

<?php
if(isset($_POST['Submit']))
 {

$file = $_FILES['uploadedfile']['name'];
$target_path="upload/";
$target_path = $target_path . basename( $_FILES['uploadedfile']['name']); 
move_uploaded_file($_FILES['uploadedfile']['tmp_name'], $target_path);
if(isset($_FILES['uploadedfile']['name']) && $_FILES['uploadedfile']['name'] != "") 
{
$fileatt = $target_path; // Path to the file
$fileatt_type = "application/jpg"; // File Type
$fileatt_name = substr($target_path,7); // Filename that will be used for the file as the attachment

$email_from = "[e-mail]"; // Who the email is from
$email_subject = $_POST['hiddensubject']; // The Subject of the email
$email_message = "Name : ";
$email_message .= $_POST['name']."<br>";
$email_message .= "Message : ".$_POST['message']."<br>"; // Message that the email has in it
$email_message .= "Email : ".$_POST['email']."<br>";
$email_to = "[e-mail]"; // Who the email is to

$headers = "From: ".$email_from;

$file = fopen($fileatt,'rb');
$data = fread($file,filesize($fileatt));
fclose($file);

$semi_rand = md5(time());
$mime_boundary = "==Multipart_Boundary_x{$semi_rand}x";

$headers .= "\nMIME-Version: 1.0\n" .
"Content-Type: multipart/mixed;\n" .
" boundary=\"{$mime_boundary}\"";

$email_message .= "This is a multi-part message in MIME format.\n\n" .
"--{$mime_boundary}\n" .
"Content-Type:text/html; charset=\"iso-8859-1\"\n" .
"Content-Transfer-Encoding: 7bit\n\n" .
$email_message .= "\n\n";

$data = chunk_split(base64_encode($data));

$email_message .= "--{$mime_boundary}\n" .
"Content-Type: {$fileatt_type};\n" .
" name=\"{$fileatt_name}\"\n" .
//"Content-Disposition: attachment;\n" .
//" filename=\"{$fileatt_name}\"\n" .
"Content-Transfer-Encoding: base64\n\n" .
$data .= "\n\n" .
"--{$mime_boundary}--\n";

$ok = @mail($email_to, $email_subject, $email_message, $headers);

if($ok)
{

echo '<script language="javascript">alert("Thanks for applying")</script>;';
echo "<script type='text/javascript'>";
echo "window.location = 'http://default.php'";
echo "</script>";
echo "<font face=verdana size=2><center>Thanks for applying!!!! You file has been sent<br> to the email address you specified.<br>
Make sure to check your junk mail!<br>
Click <a href=\"ihmjobs.com\" onclick=\"history.back();\">here</a> to return to ihmjobs.com.</center>";
} 
else 
{
die("Sorry but the email could not be sent. Please go back and try again!");
}
}
}

need help!!!!!!!!