1. Make sure your primary logon on your Win98 is "Client for Microsoft Networks."
2. When you start your win98 box, it will ask for a user and password, enter a user and password that exists on the server, and has rights to both the Share and the file/folder. A good test would be to use the Administrator account, i'm sure he has permissions to your shared files.
In windows 2000 you do not create passwords for shares, you have user level security. Meaning you set passwords on the users, and grant certain users rights to the share or files themselves. As a basic rule, you should not limit permissions on the share, rather set them on the files themselves (NTFS) It is much more secure, and it's nice to keep all your file security in one place.
Hope This helps...
Dan