Family Tree PHP is developed for PHP 5 (with MySqli extension) and MySql 5.0.12 or higher. It will not run on a server with PHP 4 or on a server without the MySqli extension. This extension is default for PHP 5, but on some servers it is not installed.
For displaying photos, the GD library for PHP must be installed. For using search engine friendly urls, the Apache mod_rewrite module must be installed. On most servers this is the case.
If you are not sure about your server configuration, ask your hosting company.