For a network with low traffic, just use 128-bit WEP encrypt.
This is a 32 character code with 16 possibilities per character...
Let's see.....add the 7...carry the 5....borrow the 10......
That's 36,893,488,147,419,103,232 possibilities!
I would take someone weeks with a sniffer to figure this out....especially with a SoHo network where traffic is really low.
That and enable the DHCP to just allow the nodes that you always have on. When you add another node to make the total 5 nodes, then take the DHCP available addresses from 4 to 5 available.
-Mike