If you already have a Web of Science account, then you've got an ENDNOTE WEB account.
How to create an EndNote Web account:
PLEASE NOTE: You must be on Campus to create an account
Go to the EndNote Web page
Click on Signup for an account
Complete the form using your Mix or Groupwise e-mail
Thanks to Yuyun Wirawati, Li Ka Shing Library, Singapore Management Library, for allowing me to adapt her guide.