Hello trovador, which GNU/Linux are you using. In Arch linux I did not have any file named modules in /etc directory. creating the modules file with ntfs-3g entry also did not solve the issue in my case.
Edit: I found a work around. unmounting and then remounting the ntfs partition with rw option solved the problem in my case. This had also been discussed in Arch forum.
#sudo umount /dev/sdbX
#sudo mount -t ntfs-3g /dev/sdb1 /media/<mount-point> -o rw,users,auto
This can also be solved by setting the hal policy. In this thread you can check :
http://forum.lxde.org/viewtopic.php?f=5&t=11