Integrate with paypal on registration

I have checked all the forums and do not understand how to do this.

I want to ensure that a registering user is paying through paypal payment screens in order to complete their registration, like a membership. Registered users or members will then have access to special content.

I am using the CB login module. I want to "hook" the registration process so that after registration information is entered, I can force redirect from the registration page in my website to a page with a paypal button that will take them to the paypal payment screens outlined in the button. Once they have paid with their credit card or paypal through the paypal payment screens, I want them to return to my website registration complete page and have them be registered. I think I can do the return peice with auto return in paypal or configuring return URL on the paypal button.

But how do I hook the registration page so that it redirects to my paypal payment button page?

thanks in advance for your help.