File upload with Custom Post Type

Hi

I would like to use a meta box to add a file to a post and use it as an attachment but I can’t seem to figure it out.

Currently I’m using this code:

function save_post_bijlage($post_id, $post = null)
{
	global $post;
	$filename = $_FILES['bijlage'];
	//echo "1:" . $_FILES['bijlage'];
	print_r($filename);

	$wp_filetype = wp_check_filetype(basename($filename), null );
	$attachment = array(
						 'post_mime_type' => $wp_filetype['type'],
						 'post_title' => preg_replace('/\.[^.]+$/', '', basename($filename)),
						 'post_content' => '',
						 'post_status' => 'inherit'
	);
	$attach_id = wp_insert_attachment( $attachment, $filename, $post_id );
	// you must first include the image.php file
	// for the function wp_generate_attachment_metadata() to work
	require_once(ABSPATH . "wp-admin" . '/includes/image.php');
	$attach_data = wp_generate_attachment_metadata( $attach_id, $filename );
	wp_update_attachment_metadata( $attach_id,  $attach_data ); 

}

add_action('save_post', 'save_post_bijlage');

and:

add_action(‘admin_menu’, ‘publicatie_meta’);
function publicatie_meta() {
add_meta_box(“publicatie_bijlage”, “Bijlage”, “meta_options”, “publicatie”, “side”, “low”);
}

function meta_options() { ?>
	<input type="file" name="bijlage" id="bijlage"/>
<?php } ?>

I can’t seem to figure out the link between getting the file uploaded to the server and attaching the attachment to the post.

I hope someone can help me out.

Thanks