Can't see hard drive from remote Mac?

Hoping someone can crack this for me!
I have just set up a G4 as a server for my home network. I have added 2 additional hard drives (ATMT 300G, Empire 400G) and can read/write to those fine. This server is plugged into the back of my sitecom router and connects to the internet fine.
I now wirelessly connect my laptop (Vista Home) and Mac Mini (OS X Leopard) to same router. They both access the internet fine as well.
Next I set up file sharing on the G4, allowing Guest to view the ATMT and Empire drives as well as my public folder.
The hitch is: Only the Vista laptop can see these drives! It can see the 2 drives + public folder. But the Mac Mini can only see the public folders, no sign of the hard drives. I tried logging in as administrator via the mac mini but still can only see the local hard drive and the public folders.

I rather expected the PC connectivity to be the tricky step here
Might it be the way the hard drives are configured? (although that seems odd to me, since the G4 can r/w to them fine....)

Thanks in advance for any clues

kk

Bit more digging ... both the hard drives are FAT32. I have a third HD (western Digital 2tb) which is NTFS ... interestingly if i plug that into the G4 via USB and share, both the PC and Mac Mini can see the files (though read-only of course).
I wonder if the problem is the internal mounting of the other 2 drives, or is it the FAT32 format. I feel the need for a screwdriver to find out ... !