samba - Apr 2008 - Standalone server providing authenticated services to AD clients?

I'm trying to set up Samba on an older Solaris 9 box using the bundled
Samba. I don't want to have to build Samba from scratch. All I need to
be able to do is provide authenticate file share access to clients
that are in our AD domain.

E.g., my laptop is an AD domain client, I am logged in as myself,
AD-DOM\myusername. Samba is running on the server with user level
security. myusername exists in /etc/passwd and has been added
smbpasswd. The same password is being used in AD, /etc/passwd and
/etc/sfw/private/smbpasswd. But when I try to connect to
\\MYSUNSERVER\myusername, "it" is trying to connect me as
"MYSUNSERVER\Guest" rather than "myusername".

I'm sure this is just my lack of understanding, but if someone could
set me straight, that would be appreciated.

[global]
        workgroup = AD-DOM
        security = user

[homes]
        comment = User Home Directories
        valid users = %s
        read only = no
        browseable = no

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