Remarks

For the moment, DF is not supported with Captive-Ntfs. It mean the program that shows the disk space usage (DF=Disk Free) won't show any information about the mounted NTFS partition. If you really need this informations, you have to remount the partition read-only, with the official linux NTFS driver.
More informations about Captive-Ntfs:
http://www.jankratochvil.net/project/captive/