Installing Zip Files
You will need a zipping program to extract the downloads from a zip file. Winzip is one example. Double-click the zip file to see what type of file is inside. If the file is a .package extract the file to: My Documents/EA Games/The Sims 2/Downloads/. Skins and objects can go into the folder. Objects can be put in subfolders, while skins cannot. If you do not have a Downloads folder, create one yourself. If the the file is a Sims2Pack extract the file and follow the next set of instructions.
Installing Sims2Pack Files
Downloads in the .sims2pack format are installed by double clicking the file. The download will automatically be installed.
Installing Rar Files
Similar to the zip format, some downloads are compressed in the rar format. To install and extract the downloads you will need software that handles the rar format. This includes WinRAR, which can handle zip files too. Same with the zip files, if the file is in sims2pack format, it needs to be double-clicked and installed not just extracted.
For recolored objects, you will need CEP.