You have to setup accounts on your system to allow others to access your shared folders. If the others are using Windows 98 or others of that sort, they will have to log into their computer as the user name you make on your system.
For example, we here on my floor have a general "Guest" account and a universal password which we all use. Most of us have Win2k running so we can enter a username when asked. Win9x users don't have that option.
You can add/delete users in Computer Management. This can be found in the Administrative Tools program group. If you don't have that set to be available you can do it in Taskbar properties.
Another way is in Control Panel under Users and Passwords