I had a very similar problem. Coronaz is right on - make sure your bios can see it first off.
I suggest you get on the phone with your motherboard tech support to rule out user error rather quickly, rather than banging your head against the wall. I sure wish I had done that earlier.
Microsoft's research engineers are spending 3 days trying to figure out why Vista won't recognize my SATA drive as a valid location to install the OS. Maybe you have the same, frustratingly rare, problem.