(XP) Password set up for file sharing

Hi,

I am logged in as an administer on my PC (XP Pro).
I would like everyone who access my PC via browsing through Network Neighbor, will be prompt a user name and password.
At the moment, every PC on my LAN can freely access
the folders I have shared, which I feel somewhat
insecure.

Any help will be greatly appreciated.

Thank.
John