I have a similar build to yours, at least with the Sabertooth and i7 950. I can tell you that at first Windows was complaining about my Marvell driver and not finding the HDD I had attached there.
So, if you have your boot drive hooked up to the SATA 6.0 Gb/s connectors, try it with the standard 3 Gb/s ones. I had to download the Marvell drivers from ASUS's site and even then I had to use fdisk to see it and format it so that Windows would see it. After that, no problems.