Not sure if you got a response you are looking for, but here are my thoughts.
If you setup your Slingbox and PC/Laptop in the same network, you don't need Internet access to be able to stream content from Slingbox to PC/Laptop. When I say same network, both Slingbox and Laptop have to be connected to the same "router" or "gateway".
Also, when I say you don't need Internet access, there's a catch. For you to even be able to start watching content from your Slingbox on the Laptop's browser, you will first need to login to the "watch.slingbox.com" website. This itself requires Internet access. That's about it. Rest everything is done through your local network.
Don't know if the above explanation made any sense, let me know if you have any questions. I can try to help you.