Create User Account For Home Network User

Hi,

How do I create an account for use by another PC on a home
network? We have XP Pro, XP Home, and Vista Premium
PCs that need to read from and write to files on other PCs.
Currently, I get privilege violations when I try to read on some
folders and can read some folders but not write to them.
Sharing appears to be set up the same on all folders.
(Privileges and user accounts differ. Not sure why.) As I
understand it I need an user account to set privileges for
access over the home network.

Gary