Your XMLSocket must run above port 1024 this is mandatory and built into flash leaving port 80 not available. So if you are not on a dedciated machine, and relying on a shared host, chances are you won't be able to connect over sockets.
If this is not an issue. There is a product named patServer available at http://www.php-tools.de
Its a pure PHP socket server. I have built some multiuser apps with it. Its pretty cool.
Check it out. For true realtime multiplayer sockets are a must.