How do I allow purchase without register?

[gameower]

Or I may ask the question this way: How do I allow buyers make the purchase without filling their shipping address and other contact info?

I want to use paypal as the only method of payment for my website, and would like to make the purchasing procedure as simple as possible. When buyers make the payments through paypal, paypal forwards their shipping address to me automatically. So I think there's no need to force the buyers to input their shipping address and other contact info again in my website.

imagined solution A:
Zen-cart may have an option allow this directly.

imagined solution B:
set the status of my store as "showcase with prices", and then insert paypal's "BUY NOW" button in the description of products. I tried this way, but when I click the "BUY NOW" button, it brings me to shopping cart and prompts "Your Shopping Cart is empty".

May anybody tell me how can I make it?

Thanks.