Attach home images to fixed URL.

Hello Everybody,
Im trying to attach images with fixed url for the home page. It is 4 images for 4 posts, I’d like them to be different then the ones that are displayed in the post itself.

Function that displays the attached image of post looks:

// Post Attachment image function. Image URL for CSS Background.
function the_post_image_url($size=large) {

	global $post;
	$linkedimgurl = get_post_meta ($post->ID, 'image_url', true);

	if ( $images = get_children(array(
		'post_parent' => get_the_ID(),
		'post_type' => 'attachment',
		'numberposts' => 1,
		'post_mime_type' => 'image',)))
	{
		foreach( $images as $image ) {
			$attachmenturl=wp_get_attachment_image_src($image->ID, $size);
			$attachmenturl=$attachmenturl[0];
			$attachmentimage=wp_get_attachment_image( $image->ID, $size );

			echo ''.$attachmenturl.'';
		}

	} elseif ( $linkedimgurl ) {

		echo $linkedimgurl;

	} elseif ( $linkedimgurl && $images = get_children(array(
		'post_parent' => get_the_ID(),
		'post_type' => 'attachment',
		'numberposts' => 1,
		'post_mime_type' => 'image',)))
	{
		foreach( $images as $image ) {
			$attachmenturl=wp_get_attachment_image_src($image->ID, $size);
			$attachmenturl=$attachmenturl[0];
			$attachmentimage=wp_get_attachment_image( $image->ID, $size );

			echo ''.$attachmenturl.'';
		}

	} else {
		echo '' . get_bloginfo ( 'stylesheet_directory' ) . '/img/no-attachment.gif';
	}
}

what I would like to do is add function “if post_id=? then img src=?” instead all that there is now for those 4 images, but since i’m not familiar with php, whatever I write returns blank pages. Please help:)