Does anyone know how to restrict access to drives, folders, etc by password-only access?

I have a network with Windows XPpro as the main computer and 2 others using 98 and 95. Before I upgraded the main comp to XP I was able to allow access to the "c" drive, for example, with a password. I can no longer do this with XP and can only "share" it completely or not at all.

Anyone know how to setup these passwords?

Thanks