if all you want to do is share files from the fedora box, samba is one way you can go. Pretty easy to setup, edit smb.conf to specify which files to share, start smbd, connect to the shares from the xp boxes using one of the various ways windows accomplishes this.
when you say "network" the 2 xp boxes, do you mean that you want the fedora box to act as a firewall, so the xp boxes go through the fedora box to get to the internet? If that is so, perhaps you should explain more how everything is setup, i.e. are you already behind a router and using private ip's? In any case, iptables is something you might want to look into.