Well, I'm open to stand corrected, but I understand that myHack no longer supports installations on MBR partitioned HDD. That would exclude OS X on your current Win7 HDD. That would leave you with no other solution but use another disk, whether internal of USB external (that works for OS X, not for Win). I think I have an old 40Go IDE HDD with Win7 on it, I'll give that a try tonight after recovering a bit of space, to confirm.