I also want to use paysat....I even wrote paysat about having a payment module to be used in an Oscommerce site....they say that they doesnt support oscommerce currently. They may support it in the near future. However,they will provide the necessary code to integrate PaySat with my site.
They also mentioned about asking the technical team of oscommerce if they can modify their code to work with them or not.
yeah there is no integration guide in using third party shopping cart....
I hope someone will contribute a payment module for paysat....I wish I wish I wish.... :P