As far as I tried, sharing a folder on a network mapped drive in Windows XP or 2000 is pretty much not possible.
The closest I got was this tool called Winbolic which allows a user to create linux like symbolic links... but it won't work in Windows XP or Windows Server 2000 on mapped network drives.
Or creating a junction point by using a tool called linkd.exe from the Windows resource kit. Which also won't work.
There's a tool that does that easily called Junction Link Magic. Although that won't work for those mentioned OS.
Of course, if anyone knows otherwise I'm all ears (eyes?).