I run several servers at work (NT and 2k) and I always format the drives with the NTFS file systems. The increased security, smaller cluster size and large file allowances are extremely necessary on servers. With that said, I have Win95, Win98, and even DOS using DOS client accessing all files and folders on the servers.
I suggest you make sure that all your computers are in the same workgroup, on the same subnet, and the folders are shared with the correct permissions.
I hope that helps.

Arnie