As far as I know it's not possible to have more than one operating system installed on any one partition (unless it's a frugal installation which is irrelevant here)
Here's a screenshot of my hard drive partitions in GParted. Windows is on sda1; Debian and Kubuntu are on sda5 and sda7 respectively, as per how I labelled the partitions.
An easy way to determine what partitions you have is to open a terminal, and run the command
Primary partitions are numbered 1 - 4; logical partition numbering begins with 5.
/dev/sda is the hard drive the operating system is installed on, and if I plugged in a usb flash drive for example, it would be /dev/sdb. Your hard drive should be /dev/sda but I would check to make sure before installing grub.
So - I am still not sure if it is possible to make a triple boot with Windows-Zorin/Mint--
It is certainly possible using grub, but I don't know anything about BCD.
Where can I get the Grub2 Bootloader without BCD
Assuming your hard drive is /dev/sda, you can install grub by opening a terminal and running the command:
sudo grub-install /dev/sda
...and assuming you would install grub from Zorin as that's the Linux operating system you can boot into now, you should see Windows and Mint listed in the terminal as grub detects them and adds them to the new grub configuration file.
This would overwrite the normal Windows bootloader and you would be presented with a Grub2 boot menu when you reboot, but having never used BCD I can't say if it would overwrite that or not, although I don't see any reason why it wouldn't - perhaps Cat would know.
Edited by Al1000, 04 March 2015 - 04:29 PM.