Two operating systems, no go. Help please!

I am trying to set up a secure wireless nework in my home. Running a G5 iMac as my main machine, and two G3 iMacs. I have an old Graphite Airport router. The main machine is hard wired, but I am having trouble setting up a wireless network with the G3s which are running OS9.2.2. Any suggestions. This is a first attempt for me and it is very frustrating.