I was in the purchasing process and my laptop blacked out...I powered it up and then the browser said that I should close the browser and follow the istall wizard...I never saw the install wizard ???
Go to https://billing.microsoft.com and sign in with the LiveID you used during the purchase process. Confirm that you OneCare subscription shows as enabled. If so, download OneCare (trial) from http://onecare.live.com and upon completion, subscribe from within OneCare, using the LiveID for your subscription to activate.