You can go to http://www.chess.com/echess/create_game.html and then choose "an opponent I choose" and then in the space provided type the email address of the friend who has not registered with Chess.com yet.
envite
Sort:
Most Recent
Forum Legend
Following
New Comments
Locked Topic
Pinned Topic
Now that I am regestered, how do I envite a friend who is not regestared to play?