OK, not sure if this will help Jenny, but it might be useful for RunAmokSims.
This dates back to July last year when I was installing a user created world, but had problems with Riverview too. This is just a copy of my post back then about how I got it to work. Copying the file and renaming it just might work for you (if you are confident with doing that sort of thing.
Original post by me (on another forum)
My main problem was with Riverview. I had to download it twice before I could get it to install and then had to have a number of trys to actually install it. Now it comes up in my Sims 3 Game Launcher as installed, but still does not show up in the game. Because of this, ####'s Riverviews would not work either. So then I found the post about world files (sorry - can't remember who it was) anyway, I went into mydocuments/Electronic Arts/Sims 3/Installed Worlds and found in there a Riverview.tempworld file. So I made a copy (to be safe) and renamed it Riverview.world and put it back in to that folder. Now while I still don't have the poplulated Riverview, I can play ####'s versions.
So if anyone has had trouble with the Riverview download, I would suggest having a look in the Installed Worlds folder to see if you at least have the tempworld file.
**update - was just reading the sims3 forum to see if others were having the same prob and some are. One suggestion (and so basic) was to uninstall Riverview and re-install it. I did that and now I have all versions of it including the populated one. So I would suggest anyone having problems with the download of Riverview to keep trying.. eventually you may get it!
Norma