It depends on which option you choose. If you select "Using Yahoo! and/or another mail program, such as Outlook Express," yes, your friend or employee will need to either have or sign up for a Yahoo! ID. (If your user has questions about this ID, reassure them that it's simply a user name to access the account.)
If you select "Never with Yahoo! Will use another mail program exclusively," your friend or employee does not need a Yahoo! ID. However, this user won't be able to use Yahoo! to manage his or her email or take advantage of our spam tools, and must access email from a desktop application.