Can PHP pages be ported into Drupal "easily"? If I have a php page, just a regular webpage that php retrieves database information from, dumps it out in tables, css, divs, all that.  Is it extremely difficult to port to Drupal?

I ask because if I don't use drupal, then I have one page with all my content and presentation and model all mixed up.  If I don't, then I've either got another framework I'm using, or I'm rolling my own.

Problem is that I need to build some pages now, but Drupal is not ready.  I can't delay, so later I want to integrate them.

I was hoping for advice on at least the best way to write a page that I know will later be in Drupal.

edit:  How do I write a php page in such a way that it is best prepared for later integration?
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.