Unzip with Winrar or any other RAR application and install the packages files in the folder:
My Documents/EA Games/The Sims 2/Downloads
If you haven't any "Downloads" folder there, you can create it, but be sure to be at the right place: My Documents/EA Games/The Sims 2/, not C:/Programs files/EA Games/The Sims 2.
If you want to download objects, you have also to download the Colour Enabler Package. Make sure you have the EP stated installed if download is EP specific, or it won't show up.