ntfs mount

[J. W. Ballantine]

Ok, either I'm missing something very basic or....

I'm trying to mount a w2k ntfs file system with:
  mount_ntfs /dev/ad0s1 /C
and I get back:
 mount_ntfs: /dev/ad0s1: Invalid Argument

I'm told this is an ntfs5 file system, could it be that
FreeBSD doesn't grok this type of fs or am I missing something
really basic??

For ad0 there is only s1,s2,s3,s4; nots5 or above.

This is on a 4.10-prerelease system.

Thanks for any and all thoughts

Jim