If you are using Windows Live OneCare on your desktop, your laptop is not protected by OneCare unless you install OneCare on the laptop, too. Install the trial -
http://onecare.live.com and activate/subscribe using the same LiveID you used on the desktop to start your subscription. You can have up to 3 computers on your subscription.
If your laptop came with a trial version of another security suite such as Norton or McAfee and they have expired, remove that software first.
-steve
Microsoft MVP Windows Live / Windows Live OneCare, Live Mesh, & MS Security Essentials Forums Moderator