In outlook 2003, it was possible to have several "sub-contacts" lists under
the main contact list, each with a different name. You can regroup in a
single list all participants in an activity, or have the list of all
contributors to a charitable organization... With all the advantages of
Contacts, detailed address, automatic email address found when you type the
beginning of the name for an email to be sent, activities on the internet
with all emails sent or received to the contact...
To have that, there was on the left top side of Contacts a way to do it, a
little bit as a sub folder in your .pst files.
The migration of data between @003 and 2007 is supposed to be automatic.
Everything was permanently backed-up with the Microsoft pst backup program
and put in a special partition of my hard drive. I have 6 partitions of 20G
each. Only C is reserved for the system. This is a security in case of
trouble: I can reinstall the system without a lot of worries. It takes a
little time, that's all.
The migration went perfectly, including, I just discovered, a contacts book
of addresses with all the contacts of the different lists, listed by list,
but very incomplete.
Thanks for asking. Could you help me or tell me who I should contact to
solve my problem. It was a good functionality, and it would be a shame that
it disappeared. I am not alone in this case, I know. Could you suggest this
to Microsoft?
Alain

I had the same problem when upgrading from Outlook 2003 to Outlook 2007. The
groups are actually Outlook 2003 contacts sub-folders.

See my solution in the posts below. The sub folders and address books are
there, just not visible in the contact navigation pane.