Mouting your NTFS device on write mode.

This will mount your HD on read-only mode:

mount -t nfs /dev/da0s1 /mnt

To be able to mount your NTFS and write, you will need NTFS-3G.

Install the port:

cd /usr/ports/sysutils/fusefs-ntfs

make install

Load the kernel module:

kldload /usr/local/modules/fuse.ko

Mount the desired device:

mount -t ntfs-3g /dev/da0s1 /mnt

Alternative mounting command:

ntfs-3g /dev/da0s1 /mnt