[monokitty]

Also the Network of the G4 can see the macmini, but the mac mini network doesn't show any other computers.

This is because the Power Mac G4 1.25 GHz has file-sharing turned OFF.

System Preferences > Sharing > Personal File Sharing -- make sure it is checked off.

Is your router a wireless one? Both computer should be connecting to the same router, not different routers, even if they're all interconnected.