Since you don't have any "true" servers, you don't have a domain environment. You are using a peer-to-peer networking environment in which there is no centralized user management.
You have 2 issues you need to deal with: user access and share mapping.
User access: In a peer-to-peer environment, all computers hosting shared resources must have user accounts created on them for all users wishing to access that shared resource.
Share mapping: All computers in a peer-to-peer network must have the same Workgroup name in order to "see" the other computers on the network. However, Win98 computers have problems seeing other non-Win98 computers sometimes. They may or may not be able to find other computers by name. You can usually get around this by using the "server" IP address instead of name in the share path (but only if all computers have the TCP/IP networking protocol installed - Win2K installs this by default; Win98 does not). You do not need to "see" other computers inorder to be able to map shared resources from them (as long as you know either the computer name or IP address and the share name). If you can't "see" the host computer in Network Neighborhood, go to the Tools menu in Windows Explorer; choose "Map network drive;" Use whichever drive letter you wish; in the path window use the format "\\serverIPaddress\Sharename"
Hope this helps.