You can't - your license is for 3 computers. Plus, OneCare will not install on Windows 7. See this post: http://social.microsoft.com/Forums/en-US/onecaregeneral/thread/81996436-edad-41ba-bdfc-02fc094e2ca9 which includes information on the free Microsoft Security Essentials which will work on Windows 7. -steve ~ Microsoft MVP Windows Live ~ Windows Live OneCare| Live Mesh|MS Security Essentials Forums Moderator ~