If you need more help, see the demo code that comes packaged with the tag. We've received a lot of questions about checkboxes and radio buttons, so we decided to include some information on how to make those work in these instructions. Checkboxes work just like any other form field - insert them into your PDF form, and set their default value to 'on'. Then, make sure that your application inserts 'on' into the database if the checkbox is checked. Acrobat will automatically check or uncheck the field accordingly.
Radio buttons are actually easier.
Just create a series of radio buttons with the same field name, but different values. Acrobat will check the button that has the matching value.