a) remove (disconnect) the mint drive.
b) Install Win7
c) reconnect the Mint drive, and makae sure it's set as the primary boot device in the BIOS.
d) Boot into Mint (Win7 won't be available yet).
e) run "sudo update-grub" .. hopefully that will find Win7 and add it to the GRUB menu .. if not, we'll fix that manually.