Instructions
Download clothing from a custom content site such as The Sims Resource or Parsimonious. When you download the file, a box will pop up asking you to either "run" or "save" the file. Click the "save" button. If you are currently playing the game, close it down now. You cannot have the game running while you are installing new content.
Save the file in the appropriate folder on your computer. The creator of The Sims 2, EA Games, already has a folder installed in the game that is designated for custom content downloads. After you install The Sims 2, the game creates a folder for you in the location "C:\My Documents\EA Games\The Sims 2\Downloads." If this is your first time downloading custom content to your game, you may not have this folder yet. If you do not have this folder, create it in this location. This the folder in which you will save your new clothes for them to show up in your game.
Open the file you just downloaded. When you download a file, it will typically be either a package file, a zip file or a Sims2PACK file. A package file will automatically show up in your game once it is added to the Downloads folder. Don't need to do anything further with package files. A zip file is a compressed file that needs to be unzipped before you can use it. Use Winzip to extract all the files directly into the Downloads folder. Open a RAR file by using the program WinRAR. The Sims2PACK file will be installed into your game when you double-click the file.
Play your game. After you've installed the clothing, it will now appear when you create a new family or when you travel to a community lot to buy new clothes.