If you plan to use PHP applications on your site, my first advice to you is to make sure that the 'register_globals' option is disabled. That option is one of the easiest ways for a hacker to break into your site and gain full control over its contents.
To see what is your site's PHP configuration in general and in particular whether 'register_globals' is On/Off you should create a file 'phpinfo.php' with the following contents:
<?php
phpinfo();
?>
and upload it to your site.
Then open in the browser the URL to the 'phpinfo.php' script:
http://www.yoursite.com/phpinfo.phpSearch for 'register_globals' to go directly to the appropriate line.
In case 'register_globals' is On, ask your hosting provider to disable it.
I think it is a good idea to remove the 'phpinfo.php' file once you are done with it - no need to show to the world the details of your site's PHP configuration.