Instructions
Download the "Sims" clothing pack you like and save it to your "Sims" folder, which is usually something like "C:\Program Files\EA Games\The Sims 2\Downloads."
Double-click the file once the download completes. This will launch the "Sims" installer.
Follow the installer instructions to add the clothing to your "Sims" library.
Start your "Sims 2" program by double-clicking its icon on the desktop.
Enter buy mode and browse through your catalog of items. You may need to click individual items to see their downloaded counterparts, as many created items are simply clones of existing ones.