The ET documentation stinks so hopefully this will help someone hook a form up to a Data Extension This is my first GIT post, so if something doesn't work, contact me and I'll fix it. It works for me, so if it doesn't work for you then I probably just explained something wrong or left something out.
Ajax.js requires jQuery, so don't forget to include it in your area. This file is not really necessary, it just allows you to display a message to the user without leaving the page. It would be much easier to just have the handle-et-data.php display a message, but this is nicer.
For a tutorial go to http://www.riptide7.com/connect-form-to-exacttarget-api-data-extension-php
Here is the ET Fuel SDK https://github.com/salesforcefuel/FuelSDK-PHP