The only way to do this is to restrict the number of groups they can access. Go into administration control, select the administrator you wish to change (or create new). Leave only the groups you want them to access in the 'editable groups' section. They will now only be able to access these groups.
You may also want to stop them being able to edit their own user ID, scroll down on the edit administrator page and remove the tick from the 'Administration Control'.
All other restrictions you want can also be changed from this section, If you only want them to be able to change passwords in the given groups, then remove all other ticks on the page except the 'Add/Edit users in these groups' selection.
