You can have up to three computers on a One Care subscription. To add One Care to another computer you can install from here -
http://onecare.live.com/standard/en-us/install/addcomputerinstall.htm To activate, open One Care, select "Subscribe" and enter the Live ID and password associated with your subscription when prompted for a Live ID.
If the operating system on your new computer is Windows 7 you cannot install One Care on it as it is incompatible. You can use Microsoft Security Essentials for malware protection -
http://www.microsoft.com/security_essentials/ Jim
Microsoft MVP Consumer Security - Forum Moderator - Live One Care - Live Mesh - Microsoft Security Essentials