Simple Access to resorces?

I am new to using win2000 pro and have set up a small home network using tcip and allowing full access or so i thought. from my win2000 station i can access all computers in the workgroup but they can not access my main computer that is using win 2000 pro. during setup i entered no passwords to allow full access to all shared resorces from any user on the net but when i try and access from another station win2000 wants a user name and password where did this come from and how do i stop it i have granted full permissions to all users and this does not seem to make any change still no access to my win2000 unit what am i doing wrong and how can i resolve this?