The key has to be activated on: http://www.thesims3.com/registeragame.html . Then you may download the game from Origin using the same login and password as on thesims3.com.
Embrace the Supernatural
Enter the mysterious town of Moonlight Falls where strange things happen by the light of the moon. Create supernatural beings from menacing werewolves and cackling witches, to mischievous fairies and more intriguing vampires. Then stalk the night, use your wand to cast spells, claw the furniture and more. You can mix dozens of elixirs that can turn Sims into zombies or transform them into gold. Share your enchanted brews with any friends who have The Sims 3! Spooky surprises are in store for you in the world of The Sims 3 Supernatural!
Processor: 2.4 GHz - Pentium 4
Graphics: 128 MB VRAM - NVIDIA GeForce 6 / ATI Radeon 9500
Memory: 1.5 GB RAM
Disk space: 7.1 GB HD
System: Windows XP SP2 / Vista SP1