Question regarding downloading FF

Ok, so I reformatted the other week, and have since installed Steam. My account has HL2 and other games acivated on it, but not installed on my pc.

Can I download (or is there anyway to) the SDK thing and FF without a game (Hl2, CS S etc) actually installed on my pc? Or do I have to download or install one of them (for eg HL2) to be able to download SDK, and then to be able to download FF and play it.

Thanks.