Using the Windows 4.3.1 CGI binary under apache 1.3.27 and IIS 5.0, the fopen function crashes when used with a HTTP URL that 404's and is more than 30 characters in the path part of the URL. When the path part is 30 or less characters it doesn't seem to crash.
It has done this on two machines running Windows XP with Apache 1.3.27 and one machine running Windows 2000 with IIS5.

The following will crash the apache process handling the php script:

function readDataFromURL($url) {
  $fp = @fopen($url, "rb");
  if ($fp) {
    $data = "";
    $buffersize = 1024;
    while (!feof($fp)) {
      $thisdata = fread($fp, $buffersize);
      $data .= $thisdata;
    }
		
    return $data;
  } else {
    return false;
  }
}

$url = "http://127.0.0.1/asdfasdfasdfasdfasdfasdfasdfasd";
readDataFromURL($url);