If you create a new account, it will allow you to select an @outlook.com email address. There is no ajax on the account name, you'll have to enter the captcha to know if your chosen email address is available.

  - Click your username in the upper right, click sign out
  - click the 'sign in' button on the next page
  - click the white 'sign up' button on the bottom left
  - see @outlook.com text box four entries down