Can't Remember How To Open Sims 2 Package Files

You need to extract them (try 7-Zip if WinZip isn't working) then put them in a folder called "Downloads" inside your Sims 2 Docs folder. If it doesn't exist, just create it. This installs them into your game. You have to turn CC/Mods on in game too.

If you mean to open the files themselves to edit them, you need a program called S2PE. That's got a bit of a learning curve though.