I'm a bit confused on where you are at with this.  I'm assuming you have successfully joined the client machine in question to your SME domain.  If this is the case, log into to your client a standard user account, open a command prompt window, and issue the following: 
c:\net user greg
User name                    Greg
Full Name                    
Comment                      Built-in account for administering the computer/domain
User's comment               
Country code                 000 (System Default)
Account active               Yes
Account expires              Never
Password last set            5/15/2001 1:40 PM
Password expires             Never
Password changeable          5/15/2001 1:40 PM
Password required            Yes
User may change password     Yes
Workstations allowed         All
Logon script                 
User profile                 
Home directory               
Last logon                   11/29/2001 9:05 PM
Logon hours allowed          All
Local Group Memberships      *Administrators       
Global Group memberships     *None                 
The command completed successfully.
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(remember to replace greg with what ever username you are using)
Note that I'm(i.e., username greg) logged into my worstation under the local windows group Administrators.  As should be given my setup.
To verify that SME is setup correctly, open a terminal on your SME box and issue the following command:  
[root@server root]# testparm | grep domain
        allow trusted domains = Yes
        domain admin group = @domain_ad
        domain guest group =
        domain logons = Yes
        domain master = True
        winbind use default domain = No
Note that on my server, samba is using the group domain_ad as the domain administor group.   My SME user account greg is set to be a member of the SME group domain_ad.
Hope this helps.
Greg