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.

Share the Story of Your Sims’ Rise to Fame! 

Live the rags to riches story with your Sims while being connected to your friends! Experience the rise to stardom as your Sim performs on stage from one venue to the next. And for the first time, The Sims 3 Showtime introduces social features, including SimPort, an all-new feature that lets you send your Sims to a friend’s game! There, your Sim can perform at your friend’s venue in front of your friend’s Sims! You will also be able to post messages and screenshots on your friends’ walls.

Minimal requirements:
 

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