To protect your NT,
- don't keep it :=)
- install last Service Pack (Not SP6, it is very buggy). There are exploits working on NT 4 SP5.
- setup boot on C only
To read/write on NTFS partition from Dos, you can use
NTFS driver.
To change NT password, you can use chntpw.
To crack NT password, you can use L0pht cracker.
NT exploits (BeAdmin, BeSysAdm...) can be found everywhere.