The best part about XML is its required well-formed nature. Worst comes to worst, you can create you're own XML handling. I have done this once on PHP4, but as soon as I could use (I think it was) the DOMXML library I dumped the ones I created. Why reinvent the wheel.
I don't have this code anymore, but I recall it being simple pattern matching. It did require a full load of the file so it wouldn't work if the file was too large to handle (at the time, about 64mb in size).
As Indegoesdr mentioned, there are a lot of XML handling functions in PHP.
If you're on PHP4, you'll be looking at DOMXML - you'll need the libxml library if I'm not mistaken to use it. If you're on PHP5, look into the DOM - simplexml can be converted to and from DOM if I'm not mistaken. DOM is also enabled by default in PHP5, but can also be disabled.
As of PHP 5.5, the MySQL library has been officially deprecated. It is recommended to move to either MySQLi or PDO libraries for your mysql connectivity. See here for help choosing which interface you prefer: http://php.net/manual/en/mysqlinfo.api.choosing.php