$host = "somedomain.com";
$link = "/somepath/";
$post = "param=value¶m2=value2";
$lenght=strlen($post);

$so=fsockopen($host, 80 ,$errno,$errstr, 10 ); //Обработку ошибок я вырезал для удобочитаемости
fputs($so, "POST $link HTTP/1.0\n");
fputs($so, "Content-type: application/x-www-form-urlencoded\n");
fputs($so, "Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms-excel, application/msword, */*\n");
fputs($so, "Accept-Encoding: gzip, deflate\n");
fputs($so, "Accept-Language: ru\n");
fputs($so, "Connection: Close\n");
fputs($so, "HOST: $host\n");
fputs($so, "User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)\n");
fputs($so, "Content-Length: $lenght\n");

while($data=fgets($so)){
  //Здесь получаем ответ
}