before you do what Adalae above said, on a mac, go to terminal, type in
chflags nohidden ~/Library
then hit command shift g, and type in ~/Library/application support/techniclauncher/tekkit (or technicssp depending on what you want) and go in the texturepacks folder and drop the zip file into it, then go in the game and select it from the "texture packs" option on the main menu
:)