If You installing Windows on a HDD whare Linux already intalled.
There is not a lot of reasons for this, in general installing windows its not a good idea (my opinion)! But if You really want this! This is the way to do it!
After Windows installation is complete. Boot live Linux Mint from USB flash or from DVD-ROM... and open terminal.
If You tray something like this (this worked on Debian squeeze, and I believe it sill works):
$sudo grub-install /dev/sda
On Mint this is what you will see:
grub-probe: error: failed to get canonical path of /cow.
Path `/boot/grub' is not readable by GRUB on boot. Installation is impossible. Aborting.
To fix this, mount rootfs. You need to specifay not only device ,bud path to mounted rootfs.
Enter something like this:
$sudo grub-install --recheck --root-directory=/media/mint/ac61ecb9-7b20-4d94-b9e2-9b1ece015459/ /dev/sda
Grub-probe will still complain ... bud its not important, cause grub will be installed successfully.
Now reboot (remove live cd or flash). Now You will not see grub menu, and Linux will boot up.
So ,You need to update grub:
And now all OS available in grub menu!