samba - Mar 2005 - Add machine script failure (Samba 3.X/Suse 9.0)

New to Linux/Samba and would appreciate some assistance with what is
probably a simple fix.

My smb.conf contains the following:

Add machine script = /usr/sbin/useradd -d /dev/null -g machines -c "machine
account" -s /bin/false %u

When attempting to join a domain on either an XP Professional or 2000
Professional machine (firewall and antivirus turned off), I am prompted with
the sign on screen.  Using root and its associated samba password, Windows
displays "The user name could not be found".  I thought to add the
machine
manually in linux using the above script inputs but substituting for %u the
computer name (lwgtp) followed immediately by $.  The result of this attempt
is "useradd: Invalid home directory '/dev/null'."  The group,
machines, does
exist as does /dev/null.

Any assistance will be appreciated.