如果要查詢所有容器下的user,用DirectorySearcher 

DirectoryEntry objDE=new DirectoryEntry("LDAP://yourserver","Administrator","pwd",System.DirectoryServices.AuthenticationTypes.ServerBind);
System.DirectoryServices.DirectorySearcher mySearcher = new System.DirectoryServices.DirectorySearcher(objDE);
mySearcher.Filter = ("(objectClass=user)");
foreach(System.DirectoryServices.SearchResult resEnt in mySearcher.FindAll())
    {
        Response.Write( resEnt.Path+"");
    }