Body Shop ships with the game. It is no longer available on the EA TS2 website. If you don't have the game ... sorry. Outa luck. If you do have the game. Body shop will be found on the start menu under EA Games/The Sims 2/
I think Bodyshop is also available at http://www.gamespot.com/pc/strategy/thesims2/index.html?q=sims+2
If you have the game, do not install the downloaded version (which is a stripped down version anyway). Not only will it not work, but sometimes it interferes with how the real bodyshop works. (I had to uninstall mine to get the thing to get the full version to work. It gave me error codes until I did.)