How to give premission to a Active directory group?

Guys,
      Only admin group users are able to view the reports from my reporting services server and as we know its not good to add lot of people in that group. Is there a way I can create a separate group with limited previllage and allow them to view these reports

My co. also have a active directory group for the people who would like to use these reports. Is there a way I can specify that group name somwhere in the config file.

Do we something similar to the one we have in webservice config file I see the authentication section, but no where  I see the authorization section.

  <authentication mode="Windows"/>
    <identity impersonate="true"/>

    <!--  AUTHORIZATION
          This section sets the authorization policies of the application. You can allow or deny access
          to application resources by user or role. Wildcards: "*" mean everyone, " " means anonymous
          (unauthenticated) users.
    -->
    <authorization>
         <!-- Allow the following users within White house:         
    Clinton Strollo (domaon\uid)
    George Bush (domain\uid)
    
Allow active directory group as well
   -->
    <allow users="MSFT\DDbio,MSFT\biodd" roles="MSFT\IT-Team"/>

            <!--  <allow     users="[comma separated list of users]"
                             roles="[comma separated list of roles]"/>
                  <deny      users="[comma separated list of users]"
                             roles="[comma separated list of roles]"/>
            -->
    </authorization>




Thanks,
Dharm