In Active Directory Users & Computers you can select multiple user objects
to add to a group. Go to the group you want to add the users to and select
Action->Properties. Go to the Members tab and click Add. Type or select all
the members you want to add to the group. If you type the members separate
them by semi-colons. Click OK and then OK on the property page. All the
members you selected should be added or you will get an error message.