Windows Sharing prompt

Need your help. A few computers in the same network but different workgroup. Each computer have a directory that
shares to everyone. By the way they are windows xp & 2000 o.s.

Question is why some computers can directly view or open their sharing directory but there are some computers prompts
you for the users and password. Can you all give me your view on this? We do not want the prompt for users & password, is it possible?