The Trust (or Security {my own term; Trust seems to used all over the program for various things}) level of the entire Network for the machine with NIS2009 on it are as follows:
FULL TRUST
Adds the network to the Trusted list
All traffic that your computer receives from a Trusted network is filtered and allowed through firewall. However, known attacks and infections are still monitored. You should select this setting only when you are sure that the network is completely safe.
SHARED
Adds the network to the Shared list
All traffic that your computer receives from a Shared network is filtered. Only shared resources on your computer, such as files, folders, and printers are allowed. You should select this setting if you want the firewall to protect you from all traffic except those that pertain to file and printer sharing.
PROTECTED
Adds the network to the Protected list
A network is in the Protected Trust Level when it has not been classified as Trusted, Shared, or Restricted. You remain protected from known attacks and all unexpected traffic.
RESTRICTED
Adds the network to the Restricted list
The devices that are on Restricted network cannot communicate with your computer. However, you can still use the network to browse Web sites, send email messages, or transmit other communications.
If you change Laptop A to a Restricted Network level then Laptop B would no longer be able to communicate with Laptop A. Laptop A would still be able to do it's proper communications (email, surf the seb, etc.) but none of the external devices on the network would be able to communicate with Laptop A. This is the tightest control schema that the Smart Firewall offers. Restrictions can be further enhanced by creating manual rules in the Firewall's General Rule database.
Note that the Network Trust level is actually how the local machine is allowed to see and interact with the external network. In your example, setting Laptop A's level to restricted would not affect how Laptop B interacts with the network; only how B interacts with A.
Does this help any?