Won't even install Sims 3 Generations

I bought the Sims 3 base game and have downloaded expansion packs from games4theworld, I'm trying to install the first EP (Generations) I have got to the stage now where I have got the 'Sims 3 Generations Installer' along with the icon, when I double click the installer icon nothing happens.

Do I have to download The Sims 3 from here or can I use my store bought game?

Thanks in advance

Did you follow the installation guide for mac?
Also, an original copy of the base game if perfectly fine, so that isn't a problem.

I think I've found out the problem, I used a different extractor program instead of using StuffIt.

Yeahh, if you're not using that specific version it won't work, it's mad.

Right, guess i've got to go through it all again