Welcome to WebmasterWorld Guest from 18.104.22.168
Your best bet is to place a form on your site that posts to another site which currently has all the code done of registering done. They will give you credit and give you a kick back.
But if you really want to do all that work don't let that stop you from coding the whole thing yourself. It can be very fun. :) I have done it several times for several companies over the years.