I work with too many Mac people to need a forum so I don't know. You might try the forums on macrumors.com and in Apple's support section. They seem to be well populated the few times i've followed links into them.
As your question about mounting a drive:
1) On the G4, make sure "Personal File Sharing" is turned on in the Sharing System Preferences (note the afp:// url below the services list).
2) On the Mini, go to the Finder (click the desktop or the Finder icon (the smiley face) in the Dock) and use the Go -> Connect To Server ... menu item (or command + K).
3) Enter the afp:// URL (it's IP address/hostname) to your G4 and click Connect.
4) Login as a user or as a guest.
If you login as a user, it will let you select what drive/directory to mount. Then it is treated just like a drive as far as the Mini is concerned.
I think there is a way to use the mount command at a command line (mount afp://... ?), but i'm not sure on that.