Do you hope to make a dual boot setup by taking what is in Virtual Box and putting it into the NTFS partition?
I assume so given you mention grub specifically. Copying data out of VirtualBox is simple, you just create yourself a shared folder and map it to something, maybe the mounted NTFS partition. I usually mount my Home directory.
If you want to do what I think you do, then its going to be tough, or easy. I would use something like
Drive Snapshot from within the Virtual Machine and snapshot it to a file and then recovery it back to the partition but it usually deals with snapshotting to drives as opposed to partitions. Plus you'd need to try and run it in wine, which I've not tried to see if you can snapshot it back.
Now I'm thinking about it, its not easy.