I had this problem. I clicked the start button on the lower left of the computer screen, clicked programs/all programs button, clicked the sims 2 double deluxe (or whatever game you have), then clicked sims 2 body shop. when the body shop is loaded, click create parts then create clothing, make-up, whatever you want to download, and when that loads, click the article of that type you want to download, crate a project name for it (it can be anything. you never have to use it again), click the export button at the bottom, and then click where it will appear in. If it is clothes you can clicke everyday, formal, etc. then click the import to game button. Now go to the sims, click enable custom content at the screen before you choose a neighbourhood, and it will appear in the game. I'm sure there are other ways but that's the way I did it and it works fine for me!
PS. Sims 2 Body Shop should be automatically downloaded when you download the sims game you have. I didn'y download body shop but it was on there.