Most login forms will set a cookie. So you should use a HTTP class like Zend_Http that can store them for further requests. It's presumably as simple as:
$client = new Zend_Http_Client();
$client->setCookieJar(); // this is the crucial part for "logging in"
// make login request
$client->setUri("http://xbox.com/login");
$client->setParameterPost("login", "hackz0r");
$result = $client->request('POST');
// go scraping
...
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…