product delivery script

Hi anybody know how to automate product delivery after paypal payments , I know paypal has option to show a page when buyer pays using "Buy Now" button , also there are services like ejunkie that do that , but I am looking for a script that can do that without using any third party service ...

would love to get your suggestions guys !

For my digital download I use Interspire Shopping Cart which allows automatic product delivery after purchase. Works great.

I know that you aren't looking for a service. But if you can't find a script. I find Payloadz better than ejunkie.

I use DLguard.

It doesn't rely on a complete shopping cart site.
You can insert BUY links anywhere (WP-posts, salespages, etc.)

DLguard will provide the code for the purchase-links and takes of care of download-links once payment is made.