What you are trying to do is to secure your wireless access point so that only your two computers can connect to it.  You do not want some one to be able to park in front of your house and connect to your wireless network.  You can do this by enabling WEP and setting up a password.  You can also use MAC address filtering on the router.  You also want to change the wireless settings on your 2 wireless computers to not allow ad hoc connections.  This will keep unwanted computers from connecting to your network.  Then you protect your computers from attack across the Internet you need anti virus and a firewall on each computer.

NVDave will also tell us that the above steps will not completely protect you, but it will at least give you a basic level of protection.