Ok I wondered about the same thing. So I take it you will get the option (in the games overview of steam) to install it once the game is released?
And a related question: I installed the steam program in my "c:\program files" directory. But when I pre-loaded the game, I didn't see an option to select a download location (nor install, but I guess thats answered above?), instead it apparently also downloaded the game there.
That is a bid bad because I would rather have downloaded the game to another drive partition which has more space left. Will I be able to (preferably) move or delete the pre-loaded game to get the disc space back once I have installed it?