Is there a way now to interface my paypal with your sign up form, so my customers can order?

The business registration form has to be filled up by the business owner (or by you on their behalf) after they've made the payment.

If you are trying to set up payments through PayPal, PayPal gives you the option at the time you are creating your buttons to add this link or any other link for your clients to either purchase and item or download a software, etc.

Please see this screenshot on how to set this up:
http://screencast.com/t/kw1PCuOb2C