Installation help?

I read the guide, and I am confused or missing something.

Step one says to install the base game and at least one expansion. Once
you've installed the base game and you then try to install an expansion, it
will only let you install that expansion if you let it update the base game.

Since this wasn't anywhere in step one, and we are supposed be exact with the
directions, I didn't know if something had changed, or if had always been that way, and just wasn't mentioned.

So, I tried it after letting it update, and the fix didn't work. Of
course, if I don't let it update, then I can't install at least one expac, so
I'm assuming it wont work that way either.

Advice?

Thanks....Trying now. =]