How do we recover Outlook categories from a registry backup?

We did the big no, no! We rebuilt a machine and forgot to backup or export
the Outlook categories. Now our new reinstallation of Outlook does not have
any of our old categories. Fortunately, we do have a recent backup of our
Windows registry. However, the backup is of the whole registry and not just
the Outlook registry key for the Outlook categories. Obviously, we do not
want to restore the whole registry that existed prior to the rebuild. What
do we need to do to import just a portion of the registry backup, i.e., the
Outlook Categories (don't remember the key)?

We really hope this is possible since we had hundreds of categories and
wouldn't even know where to start to find and re-enter them. Isn't there a
way to rebuild the categories from the Outlook .PST file we have now used to
restore our contacts following the rebuild? It would seem logical to have a
utility that would harvest all the categories currently existing in the .PST
file and recreating them as categories in the new Outlook installation?

We would really appreciate any help anyone might have !!!