Sorry, I didn't see your comment on my wall until now. Have you made any progress on your quest for PayPal integration with your Ning site? Please message me with your thoughts if you would like to discuss this further. Thanks!
It would be involved. I would have to make 3 custom pages and map your network around these pages. Then I would have to show you how to set it up in PayPal and get the PayPal code to work on these pages.
It would take a week to complete. I do not know what your budget is. My time is very limited and my rates are competitive.
If you interested you can call me on Monday afternoon to discuss.