I worked out another way to set up dual booting from windows
This will install to an external USB hard drive or flash drive.
This way there’s no need to be scared that you will damage your windows set up. This should work exactly the same on a linux VirtualBox setup
In windows install VirtualBox
and expansion pack- VM VirtualBox Extension Pack both fromhttps://www.virtualbox.org/wiki/Downloads
Make a new windows virtual disk 10GB, will be fine. Accept all the defaults except memory set to at least 1GB
Down load your Linux Mint ISO and set this as a boot disk via settings, storage, IDE controller add cd/dvd device.
Start the virtual machine and wait for the Mint Desktop
Insert your external USB hard drive or flash drive and click on devices and tick the new drive.
Wait while the drive is recognised – you'll see a popup on windows saying the device driver is now ready.
Start the installer.
Language setup as required then continue
Preparation to install - continue
Unmount = YES
Next chose - Erase disk and install Linux Mint
Select drive usb drive required, then install now
Answer all remaining questions
Once completed power down the virtual machine
Then reboot computer and chose your usb drive from the bios or boot manager. You will not have your original operating system available from grub this time but will boot straight to Mint.
Once rebooted with the external USB hard drive or flash drive removed or powered down the original OS bootloader will start windows.