Sharing between Vista & XP & XP

This is almost like another post with the problem, but with a strange
twist. I have resurrected an old Win2K machine and upgraded it to XP
Pro. When all the updating and whatnot was done, I created two folders
- one on each drive (C and D) called 'Public_C' and 'Public_D'.

I do this so I can pass items back and forth directly to storage drives
on different computers. My problem is that files in the Public_C can be
seen/written/read/deleted by anyone on my LAN (5 computers including
Vista & XP). Public_D will ALWAYS give an "no access" error to anyone
who tries to enter the folder from any computer.

Any ideas on this one? The permissions were applied exactly the same on
the C and D drives.

GP