Can PHP pages be ported into Drupal "easily"?
Well, you don't really. If you are accessing the database in anyway you should be using the Drupal database API. There are a lot of things that you should do using Drupal API's if you are going to use Drupal. However, with that said, you can run any PHP you want in any Drupal node. So, there is nothing special you need to do in order to write your PHP code to work within Drupal. However, you really should think through your implementation before you being and determine which parts should use Drupal.

Also, it only takes about 3 minutes to setup a Drupal installation. So, you could just setup a dev site in no time flat and develop inside that. Even if you don't have a server you can download a few applications that will act as a server like XAMPP which will give you Apache, PHP and MySQL so that you can install Drupal and begin working.