Thanks for the reply. I think the PHP code in the book should work just fine for me. The nice thing about PHP is that it seems to be very mature, and also backwards compatible with older versions. I was mainly wondering if there were breaking changes to any of the external APIs used (such as Paypal, Stripe or Authorize.NET). I guess I shouldn't be too concerned, as most of the payment providers keep things pretty consistent and/or provide excellent up-to-date documentation.
On another note, I was able to find some of the old documentation and sample sites for Site Server Commerce Edi