Ad extra field to magento checkout

Make two extra fields in checkout and shopping cart those fields have to match , like when you registeren and have to type in passwordt two times. I am using onestepcheckout and I want to be able to enable disable the fields. ALso the fields needs to be required ( so customer must fill in something) See attacment for explaination Only bid if you sure you can do the job Regards Julio Rosier