I have dual boot (win7/ubuntu 12.04) system. I want to mount a specific folder (namely the Dropbox folder) from my windows partition in my home directory.
Unfortunately, I am not able to do that.
As far as I understand, I can not 'directly' mount only a folder from a partition, but have to mount the entire partition first and then mount --bind the folder.

If I mount the partition writable, there are no problems. But if I mount the partition with

sudo mount -r /dev/sda2 /mnt/win

and afterwards try

sudo mount --bind -w /mnt/win ~/Dropbox/

It says

mount: warning: /home/ope/Dropbox/ seems to be mounted read-only.

I also tried it using /etc/fstab, following the solution given here.
The relevant fstab lines look like this:

/dev/sda2 /mnt/win ntfs user,ro,umask=0222,defaults 0 0

/mnt/win/Dropbox /home/ope/Dropbox ntfs-3g rbind,user,rw,defaults 0 0

#/mnt/win/Dropbox /home/ope/Dropbox ntfs-3g rbind,user,rw,umask=0222,defaults 0 0

The last two lines both create only a read-only mounted folder.
Is there antything I am missing ?
Thank you very much for any hints.