Right click the D:\ drive and select the "Explore" option. (where d is the letter of your CD rom drive) This should bring you to a list of folders. The go to the "Patches" folder and then the "res" folder. There, you should find three new faces and skins. I believe these skins are those of the creators/designers of The Sims. The names of the skins are:

Bobby

Dennis

Werner

The location, to be exact, is "D:\Patches\res"

You can copy these into your game data folder (C:\Programfiles\Maxis\The Sims\ Game Data\ Skins) and they will become playable characters in the game!

I'm surprised nobody found this out before I did! I've been playing for years and this is the first I've ever heard of hidden skins!