Once you have downloaded the 3DModels-LucaPresidente-1.2.1.zip file from http://sourceforge.net/projects/sweetho ... els-1.2.1/, open it in your system and extract the LucaPresidente.sh3f file it contains.
Launch Sweet Home 3D, choose Furniture > Import furniture library menu item and select the LucaPresidente.sh3f file you extracted.