pick a folder, any folder, and then rightclick it and hit PROPERTIES, then the SHARING tab, then ADVANCED SHARING and you should be able to sus it from there.
Also, check your firewall settings. You can either share it to everybody, or create a user in the control panel with the same name and password of your XP login if you want to be a bit more security savey!
Let me know if that doesnt fix it but thats the first step