Where’s My Network and Workgroup

I have three Macs running 10.4.8, two have My Network and Workgroup as sub-categories to Network in the Finder, one does not and simply displays computers in the first column in the same way that 10.3.x does. Does anyone know if there is a way to turn on the Network Grouping function? David Pogue says in Tiger Missing Manual that it depends on size and complexity of your network, which sounds like a nice way to say "It doesn't always populate...." Since all three computers are the same net, if complexity is the key, I would think all three would show My Network and Workgroup. Macs that do: Intel iMac and G3 iMac. Mac that doesn't: PowerBook G4.