On the PHPFreaks.com website a new tutorial (by Ben Smithers) looks at interfacing checkboxes in your application's form with a backend database.
The concept is actually pretty simple. It involves naming your checkbox as an array and the use of the IN mysql clause. This tutorial aims to give a simple example in the hope that, next time someone asks, I can point them to a tutorial rather than explaining all over again.
They include the database structure, insert statements and the code needed to pull and push the information for the checkboxes.