Cannot Network Macs!

HELP! I have been using macs for years and have always been able to get round little issues with getting them to see each other and connect. But today I think my mojo is low.... I just can't get my macs to see each other - I have a G5 tower (os10.4) a powerbook(os10.5) and a macbook pro(os10.4).... (yeah I'ma graphics monkey..) and for some reason none of them can see each other / won't network together. It's driving me nuts because I need to share files between the computers. PLEASE HELP!! (I'm on a BT Home Hub2 network.)

Thanks! :Blushing: