When you install them and open the game, do they show up there? Because I have a similar problem;
Whenever I try to install a few items (including most-importantly the 2 collector's cars and Riverview), it says they got installed, and then when trying to open the game, the launcher pops me an Error window, saying it has to be closed, and the items aren't in the game. If I re-open the launcher, it will show them as not installed.
Many people are having a similar issue (I checked yahoo!answers and the official forums, no solution so far.)
It's like the old saying: when you need a patch, it takes longer to come out.