.iff Objects go in here
.iff A downloaded house will overwrite an existing house
.fam Downloaded families
.iff Objects can also go in either of these folders
.flr Floor tiles which appear in BuildMode
.bmp BuildMode roofs
.wll Wallpapers
Downloaded skins and animations
Do not use sub-folders here
Where to Put
the Downloads
Whether you are on a Mac or a PC, downloaded files go into the same folders in your game. From Livin' Large there is a UserData folder for each neighbourhood, and extra ExpansionPack folders. Always look at any ReadMe file that came with an object because it may tell you to put the download into a different folder.

Usually, objects can go into any one of three folders, where you can also organise them into sub-folders if you so wish.