mac network drive not password protected on xp

On Win XP, I have setup a mapped network drive to connect to my Mac OS
10.3. However, problem is it never prompts me for a password to connect
and goes directly to the home folder on my Mac, and I'm assuming others
on our network have complete access to my Mac too. Even if I turn off
the "windows sharing" option on my Mac, the mapped network drive on my
PC is still able to connect without password prompts-- what gives? How
do I enable protection on my Mac so PC users can't access it on the
network without a password? 

Thanks, -c