The OpenID Server example is down on the main site for OpendID for PHP.
It is reporting the following error for me (using Firefox 3.0 on Windows XP):
Warning: require_once(Auth/OpenID/HMACSHA1.php) [function.require-once]: failed to open stream: No such file or directory in /home/web/examples/php-openid/2.x.x/examples/server/lib/common.php on line 12
Fatal error: require_once() [function.require]: Failed opening required 'Auth/OpenID/HMACSHA1.php' (include_path='/home/web/examples/php-openid/2.x.x:.:/usr/share/php:/usr/share/pear:/home/web/examples/php-openid/2.x.x/') in /home/web/examples/php-openid/2.x.x/examples/server/lib/common.php on line 12