Jerry, the bad news is that throwing out the key means that you are now unable to activate a subscription. There is no way to recover it. Your best bet at this point will be to look for an online deal for a cheap copy of OneCare if you still wish to subscribe. You can install OneCare, if you have not already done so, and use it for free for 90 days, but after that you will need to subscribe by purchasing it again.
-steve