Simply because I haven't Vbox
I installed windows, created the data partition.
Then I installed linux on the free space I left on purpose.
Grub is installed in MBR.
I installed ntfs-3g even if I think it's not necessary with new kernels.
Then I mounted the systems on my linux :
mount -t ntfs-3g /dev/sda1 /mnt/windows
mount -t ntfs-3g /dev/sda2 /mnt/data
This worked so I setted up the fstab for /mnt/data
I transfered all I wanted from my windows partition so I haven't to touch it now.
My computer is mainly used as testing server, the windows is only there when some friends come and need an internet access (my server is a fully minimal debian install, this means no graphical interface at all). data is used for FTP and backup.
So I access my windows by rebooting, I don't want to load it in VM.