I'm not sure that the file system used on the different OS makes the difference. I've got an old Win98 machine (FAT32) networked (wireless) with an XP machine using NTFS.
I think Win98 always needed the computers to be in the same workgroup, not sure if XP can see machines in other workgroups, it might be able to. If the correct folders are being shared, and you have no added complexity like password protected folders, I don't know what else would be missing.
Can you 'search the network neighbourhood' to find the other machine? Sometimes a search is all that is required to get a two-way street established.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)