http://technet.microsoft.com/en-us/library/cc784045(WS.10).aspx
other info
http://forum.soft32.com/mac/Connecting-Mac-Windows-Server-2003-ftopict6839.html
Windows server 2003 can easily be a print and file server for Macs.
Here’s the thing.
The 2003 server may already be set up to serve files to macintoshes, but the
mac client you are trying to access the server with may not have the UAM
(user authentication module) installed, so it can’t authenticate and access
the share (more on that later). Therefore, the method you are using to
authenticate is incorrect because you either do not have a UAM installed, or
your macintosh is trying to use the UAM for NT4, which generally doesn’t
work properly for 2003.
Or, your 2003 server may not have the file server for macintosh service
installed. If this is the case–read below.
Macintoshes use apple file protocol to share files. Windows does not. If
you want to have your mac access files on the 2003 server, you need to
install and configure the File Server for Macintosh service on the server in
question. Once you have installed the service, it installs appletalk, apple
file protocol, and a microsoft UAM share on the server. The User
Authentication Module is what the server needs to authenticate the macintosh
to the shares on the server. If you do not have that on the macintosh
client that is trying to access the share, the user authentication method
error can occur.
The UAM for 2003 is different than the one used for the NT4 server.
Furthermore, the UAM for OS9 is different than the one for OSX. The one
available by default works fine for OS9.