This outlines what I've done to setup Samba on Linux to use the campus Active Directory for authentication and authorization. My setup was done on Red Hat 7.3, with Samba 2.2.7, but the information should be applicable to other versions.
I will assume from to this point that you have installed the samba software, and that you have the configuration files updated, using the examples below as a guide.
Start the samba daemons:
# service smb start
A domain admin will have to join the server to the domain just like a Windows server would:
# smbpasswd -j IOWA -r iowadc1.iowa.uiowa.edu -u <admin name>
# net ads join -w IOWA.UIOWA.EDU -S iowadc1.iowa.uiowa.edu -U <admin name>
Start the winbind daemon:
# service winbind start