Adding local groups to a NT Workstation

Answer:
According to the MSDN, "Only members of the Administrators or Account Operators local group can successfully execute NetLocalGroupAdd." But given than you actually have the correct rights, then the following code should work.

Option Explicit

Private Const NERR_Success             As Long = 0&
Private Const LocalGroupMembersInfo3   As Long = 3&

Private Type LOCALGROUP_MEMBERS_INFO_3
   DomainAndName                       As Long
End Type

Private Declare Function NetLocalGroupAddMembers _
   Lib "netapi32" _
   (ByVal psServer As Long, _
    ByVal psLocalGroupName As Long, _
    ByVal level As Long, _
    pPtrBuffer As Long, _
    ByVal membercount As Long) As Long
    
Public Sub Main()
   AddUserToLocal "xxx_group", _
                  "myuser", _
                  ""
End Sub

Function AddUserToLocal(ByVal xi_strGroupName As String, _
                        ByVal xi_strUserName As String, _
                        ByVal xi_strServerName As String) As Boolean
   Dim p_lngPtrGroupName   As Long
   Dim p_lngPtrUserName    As Long
   Dim p_lngPtrServerName  As Long
   Dim p_lngMemberCount    As Long
   Dim p_lngRtn            As Long
   
   ' Convert the server name to a pointer
   If Len(Trim$(xi_strServerName)) = 0 Then
      p_lngPtrServerName = 0&
   Else
      p_lngPtrServerName = StrPtr(xi_strServerName)
   End If

   ' Convert the group name to a pointer
   p_lngPtrGroupName = StrPtr(xi_strGroupName)
   
   ' Convert the user name to a pointer
   p_lngPtrUserName = StrPtr(xi_strUserName)
   
   ' Add the user
   p_lngMemberCount = 1
   
   p_lngRtn = NetLocalGroupAddMembers(p_lngPtrServerName, _
                                      p_lngPtrGroupName, _
                                      LocalGroupMembersInfo3, _
                                      p_lngPtrUserName, _
                                      p_lngMemberCount)
   
   If p_lngRtn = NERR_Success Then
      AddUserToLocal = True
   Else
      AddUserToLocal = False
   End If
   
End Function