More info about posting links (what you call "post with web site preview") here:
http://developers.facebook.com/docs/reference/api/link/
I asumme you have your Facebook APP with your permissions set, and that you're using PHP-sdk classes. Anyway, the proccess is the same for any language, just changing the way you write it. Also, you need the user Access Token with the proper permission set.
Using the PHP-sdk from Facebook, process would be:
// Load FB class, and init it
require_once("facebook.php");
$config = array();
$config['appId'] = 'YOUR_APP_ID';
$config['secret'] = 'YOUR_APP_SECRET';
$facebook = new Facebook($config);
// You set the User Access Token (you need to have it previously to this: Because you
// requested before, or because you obtain it from Facebook)
$facebook->setAccessToken( $user_access_token );
try {
// Set the link params:
if ( isset($config['link']) ) {
$args = array(
'link' => $link_url //Url to be linked
, 'name' => $link_titulo //Box title
, 'description' => $link_descripcion //Box Description
, 'picture' => $link_foto //Photo to be posted
, 'message' => $link_message //Message over the "link box"
);
// Post in the User/FB_Page wall
$facebook->api('/me/feed', 'post', $args);
}
} catch (FacebookApiException $e) {
$fbError = $e->getResult();
$result = array(
'tipo' => 'error'
, 'code' => $fbError['error']['code']
, 'text' => $fbError['error']['message']
);
print_r($result);
}
Update
After reading your answer to my comment, I think you're looking just for the CSS and the layout. You can find something to achive the post formatting here:
http://jsfiddle.net/5NYD5/3/