One of the more popular questions I see from budding e-commerce site owners is how to add a payment system to their site. They have the catalogs and shopping carts all set, but they're missing that key piece to handle the transaction. Paypal, one of the largest online payment handlers, has released a new resource to help make life easier - the PayPal Integration Center.
Along with this launch, they have also upgraded the PHP SDK they offer to a shiny, new version - 4.0. According to DynamicWebPages.de, they've added the ability to make a request without an SSL certifiicate, made installation easier, and more.
Their prefered method of installation has moved over to a PEAR-based setup, making it as easy as going to the source directory and calling "pear install package.xml". Of course, not everyone has access to the server their running on (shared hosting), so they provide another method just for them. It's still simple, but requires the inclusion of files on each execution.