It seems that sometimes it is either not possible at all to download or the download starts but not with the full size. If you encounter this problem try following:
Next to the picture at the download page of the item/sim/lot you want to download is the "add to game" button and underneath "save file".
Try to download it by clicking "save file". Once downloaded move the file to your sims3 folder and install. This usually works.
Next to the picture at the download page of the item/sim/lot you want to download is the "add to game" button and underneath "save file".
Try to download it by clicking "save file". Once downloaded move the file to your sims3 folder and install. This usually works.