You will need to provide some more information. Such as how users authenticate on the network.
Do you use profiles? Does the XP pro server authenticate users to the network?
I'd highly recommend downloading the Samba 3 book which has examples for several samba servers.
www.samba.org/samba/docs/Samba3-ByExample.pdf. You may be able to base your samba server to one of the examples. A reference guide is also available as well there. These books are also available from a samba-doc package from your Linux distro. You may already have it.