Certainly. If OneCare is still installed, you need to remove it first.
http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=663806&SiteID=2
Before doing this, make sure that you know the LiveID for your subscription as you will need to activate OneCare after you install it and you cannot use the key again, nor can you use a different LiveID.
Install OneCare by downloading it from http://onecare.live.com
-steve