See my post in sharing. You have to connect to the OSX machine as administrator, with administrator password and privileges. Also make sure that the external drive is formated in HFS and accepts long file names and such. I had the same problem with an external drive until I reformatted and updated the filing system on that drive. I have my external firewire drive connected to my G5 10.3 Panther, login from my G4 9.2 and am able to read, write, save, copy or anything with that drive as if it were physically connected to the G4. (WARNING: be careful with administrator access). I'm sure if we had OSX server we wouldn't have to network this way but it works!
Also may have to do with the firewall and make sure to set the privileges for the external drive to read and write for all.
Hopefully any of this works for you.
