I believe Knoppix and subsequent developers of rescue type Knoppix spin-offs (such as INSERT) anticipated just such a scenario like yours, that is, using Knoppix as a rescue disk to reset NT passwords.

See for example Hack #75 in the Oreilly book "Knoppix Hacks" which explains the steps.
http://hacks.oreilly.com/pub/ht/124

An expanded explanation is here:
http://www.linuxquestions.org/linux/...s_with_Knoppix

Now, to do the above, you are going to have to activate Knoppix's NTFS write capability. Not everyone is going to agree that it is safe. I have done my trials, and believe it is good enough for rescue purposes, which is what I will use Knoppix mainly for. This is because in a rescue situation, it is often a case of taking a risk, or else lose everything by doing nothing. If you want to be cautious (I am), image the XP partition before fiddling with it.

Best of luck. And if you succeed, come back and tell us about your experience.