It may be hit or miss as far as the Vista drivers working with Windows 7.
I would shrink your harddrives free space, create another partition and install Windows 7 there first, leaving your other OS alone for now.
ASUS Maximus V Gene MB
Windows 8 X64; Windows 7 X64; Windows 7 X86
16GB Corsair Vengeance Ram
eVGA GeForce GTX 550 TI
Corsair GS700 PS
1TB Seagate SATA 6.0Gb HD