I am guessing, but don't you need GPT drivers for win7? Win 7 only supports MBR/NFTS out of the box.
I know windows won't read any of my hackintosh partitions at all and say they have errors and windows would like to format them.
Not sure where you'd find such a driver. Maybe check hackintosh sites such as Insanely Mac or TonyMacx86?
ps a quick google and I came up with this from MS forums:
How to clean install Windows 7 Professional 64-bit to a GPT - Microsoft Answers