I have to add here, that most all of TSR's stuff is in sims3pack files. I don't remember the path right now, but you can dictate where your comp will d/l stuff. If you d/l stuff from many sites you may not want to command your comp to put all d/ls into your Downloads folder of sims. Anyway, when the d/l starts, you'll see it on a bar at the bottom. When it is done, you can click on the arrow on the right and choose "show in folder" and then click and drag the file over to the Downloads folder in sims 3. You don't have to do this every time though. You can let that bar at the bottom fill up w/files and then click on the newest one which appears on the left side and show in folder and highlight all of them and drag them over. When you're completely done d/ling sims3pack files, open the launcher and install everything. Then move those files to a safe place like a folder on your desktop. Once the file is installed, you don't need anything in the Downloads folder.
In the case of a .package file follow Mrs Flynn's instructions.
I just thought of something else. It might be that the item you d/led could possibly be cloned or recolored from an ep or object that you don't have. If that is true, then it won't show up.