As far as going in your Admin CP; No, there is NOT currently an option to turn it off (i mean.. i haven't seen one.. but like all other men, i see and hear what i want to)
You can, however, remove the variable for both of those options in the template file.
First to explain Usergroups, since I currently can't find a link for you:
Imagine the usergroup as one user on your forum. You can give specific permissions/moderator access for that one user. The only difference is a usergroup has A Moderator (Person who adds others to the usergroup) and all the people in a usergroup.
All the people in that usergroup receive the permissions that the usergroup does ( i hope thats not too confusing )
As far as how to remove Who's Online:
index_body.tpl is where to go.
It has the html/variables for it.
the Usergroup link/Variable is in overall_header.tpl
Both are in your theme folder
Beware: "guessing" on what you're removing isn't the best idea. Perhapes using a wysiwyg editor would behoove you.