I had some luck using the Ophcrack Linux Live CD. They have one for WinXP and
one for WinVista/7.

I'll watch this string to what others suggest...

This may be of help too:

http://www.caine-live.net/page11/page11.html

It mentions a Hive tool. I saw it on Distrowatch.

If the key information you seek is the key supplied from Microsoft to be used at
the time of installing the XP operating system, then
if you run BelArc Advisor (free Internet download) the key will be shown on the
printout. BelArc lists all the hardware and software installed in the computer
along with much details. You have to install BelArc on the machine in question,
so you have to be able to boot the OS, install BelArc, so BelArc can analyze and
display the results.

Yes, the problem is that I cannot boot the machine. If I could, I would
not have a problem extracting this key. That is a relatively simple
process. But since I cannot boot the OS that contains the key, I need
to mount this hard drive as a slave and then use one of the keyfinder
programs to search for it in the system32 folder. This is the process I
have not been able to figure out.

If you have hard drive space install windows again in a different
directory. Better still boot from a live CD/DVD of some Linux distro
that has the kind of tools you need and use that to extract the hive
you need.

As far as I know, you can open the .reg files with a text editor. I have done
this in the past with exported .reg files. I would copy the .reg files
somewhere and just attemtp top open with a microsoft editor like wordpad.