Payment on sign up / Subscription, products will all be free

Hi there,

I have been asked to work on a project where my client wants to have an online magazine, where each article / product, will be a downloadable file, most likley of a project for the end user to print / make.

She would like to take paymebnt by means of subscription, £10.00 per year to the website, and there after all the products / projects will be free.

Can anyone help me with a way of getting a paypal / payment window into the sign up pages, and the relevant changes i may need to make?

(I appriciate it's unlikely anyone will do this for me for free, but if you could point me in the right direction for what changes to make I would be most greatfull.)

Rammer