Ensure that File and Print Sharing are installed. Control Panel --> Network, File and Print Sharing. If I remember correctly, there are two check boxes in there that need to be checked (under file and print sharing).
Verify that the PCs are both members of Workgroups that are named the same thing (such as Workgroup). This is under/near where you set the computer name. Right-Mouse-Click on My Computer and go to properties. There should be a tab for Computer Name.
On the NT Machine (it is easier here), right mouse click on a folder that you want to share data in and go to sharing. Under the sharing, choose Share this Folder (or directory). Give the share a useful name (it is how it will appear from the other computer). You will need to apply Share Permissions. By default, it will give Everyone Full Control (if you are not worried about security, this is OK).
This will allow access remotely to everything below this folder from other computers (least restrictive).
For security, you will need to apply permission to the individual files within this share (there should be a different tab for security). You can just give everyone Read/Write/Execute privileges, but do not give full control. There is a check box with something about "Replace permissions on all child objects", I would check this (so you do not need to reassign permissions on all things within the folder(s)).
You can do similar things on the Win98 PC with the Share permission, but the Fat32 file system will not allow for Per-File permissions to be assigned (so the 2nd part talking about child permissions can not be done).
It is not all that hard to get this to work.
Also, Turn off any software firewalls (or allow Windows File Transfer Protocol/Windows File and Print Sharing in the firewall). Both PCs must have IP Addresses that can see each other (or have a router that can cross IP Subnets/LANs). I would assume that your house LAN already takes care of that.
Once you have set all this up on the NT computer, from the Win 98 PC, go to Start --> Run
In the Run Window, type:
\\X. X. X. X, which is the IP Address of the NT Computer.
Eventually an explorer window will appear, in here, you should see the Share you created, something for Printers, and maybe a Sysvol folder. You should be able to access your stuff now.
Getting to the 98 PC from the NT computer might be a little more difficult, but should be about the same setup. I am sorry If I got this a little wrong (I have not worked on NT in a few years, but I am an MCSE on NT4. 0).
-Rich