How to download the furniture for Sims deluxe?

You know how you can download extra furniture off sites like SimFreaks.com? I downloaded one, but I don't know where to put the file. Does this make sense? You go to program files, then Maxis then Sims Deluxe, and it has all the files, Like ExpansionPack1, and GameData? Where do I put the IFF files in all of this? Or do I need to convert them somehow? Thank you.