I'm not familiar with Drupal, really. I can dig around the admin interface and navigate the directories and find the files that I need to just fine as well.

What I'm really not familiar with is adding modules or extending modules. The site currently takes an order and sets up recurring payments through Ubercart and uses Authorize.net as a gateway. Right now, when a payment fails, a single e-mail gets sent out to the admin. We'd like to extend it to send an e-mail to the user and let them change their payment information through another page on the site.

Authorize has a service called Silent Post URL that basically just posts a carbon copy in XML to whatever URL you give it. We'd like to accept that XML, deserialize it, parse the data, send a notice to the user and give them the page for updating their information.

So, I guess it'll be two PHP pages. One for the XML API call from Authorize.net, and then one for the page for the users' to update their payment information.

Could I just create two simple pages each handling their own tasks, or should I check out properly extending a module? If it's appropriate for me to write up the pages and not have to hook them into the module, what would be the best way to handle setting up what needs to get done?

_{(The most experience I've had with extending a PHP site has been hacking away at someone else' poorly constructed, custom framework, so if anyone has any good resources perhaps on PHP best practices that they could share through a PM or a comment, I'd appreciate It)}

_{(Also, I'm still getting the hang of Stack Exchange, so if this isn't appropriate please let me know. I'll delete it.)}