Last week, Hershel Robinson, created a Drupal module for my client (called CiviCopyAddr) to handle the copying of the primary address into the Billing Address fields via a toggled checkbox. It's located at https://github.com/hershelsr/civicopyaddr . We use Authorize.net as the payment processor. To make it work:
1. Copy the files from the github into a directory call CiviCopyAddr and copy that directory into sites/all/modules and enable the module in Drupal.
2. Set up a Civi profile with first name, middle name, last name, street address, city, state, postal code and country (if needed) as PRIMARY contact fields.
3. Add that profile to your event, membership or contribution form. You should now see a checkbox above the billing address that allows you to copy the name and address fields from your profile into the billing address fields. Note that this checkbox is a toggle so if you check and uncheck it the fields will be copied and removed accordingly. Try it out for yourself!
