integrate with ubercart

Ubercart has a lot of configuration and there are good instructions at ubercart.org, do it on a throwaway site first to get the hang of things. Set up country, site owner, products and attributes and anything else you might run across, export the whole site with phpmyadmin, fool around and if it goes wrong you can roll back.

What I want is is an email sent to purchaser with pdf invoice attached, at monthly/annual intervals, eg regular billing. I run a small web hosting outfit.

Hi, just thought I'd let you all know about a new module I just created. It allows for invoice payments via Paypal. It adds a 'Paid' flag to every module and on successful payment via Paypal (conformations come from PayPal IPN), the paid flag is checked. It's located at http://drupal.org/project/invoice_paypal

In addition, @hutch: I'm working on a module right now that would be of assistance to you. Essentially, it's a module that keeps an eye on service agreements for you. That could be hosting, support, maintenance contracts, or anything else that requires monthly billing. It would also be more convenient for your customers because they can give Paypal their payment details and they would automatically get billed monthly. This is completely offtopic in this issue, though, so if you're interested, get ahold of me through my contact form and we can talk about it via email :)