Bigfitty is correct.
For example: If you log onto your Win2K machine with the username "BILL" and then log onto your Win98 machine with the username "MARY", you will never be able to access anything on the Win2K machine because there is no user "MARY" defined on the Win2K computer.
If you noticed, when you tried to access a network resource on the Win2K computer from the Win98 computer, it didn't ask you for a username and password. It only asked you for a password. The computer was automatically using the user name "MARY".
Simply make sure that you define in the user manager all the users that you want to have access to the Win2K computer. If you want "MARY" to have access to the Win2K computer from another computer, then just create a user "MARY" on the Win2K computer.
Hope this helps.