We don't get a lot of flash experts on these forums. Your best resource for information on how to add hidden fields to flash is with a Google search using the string "flash forms hidden fields". You will get lots of information.
Bravenet provides a less than helpful FAQ article labeled Will your Email Forms service work in Flash. So for the submission part, you will have to look into Bravenet's form service yourself. Register for the free service and create a dummy form. Then look at the code it creates. You will be able to see the required hidden fields and the form submission references. Between that and Google, you should be able to figure it out.
