One of the cool things about php is that all regular html is perfectly valid, so if you just save one of your .html pages to be a .php page instead you will be able to use php code on that page. If you only need php functionality on a couple of pages you can just change those pages. If you change all of them to be php pages you will have the ability to add php code to these pages.
You will need to have a php type of site setup in DW. You can either change the one that you have now to be a php type of site or create a new DW site. Here is a link to a page on our site that has some resources for defining your site in DW as well as setting up a connection to your db.
There are also some other resources there are setting up a local dev server if you need any help on getting that part going with php.