I think the folders changed after recovering from some other non-vb problems related to partitions which involved tweaking /boot/grub/menu.lst and using testdisk.
I've been able to install a new XP on a new .vdi drive and map a new shared folder, all on the same partition as the inaccessible files. The new installation works fine and a new shared folder is accessible from both guest and host, but I can't load the old shared folder in the new guest.
I've searched the forums, but haven't seen this exactly. I'd appreciate any help.