It can't be hijacked by internet nasties like windoze address book can and you can save setup time by importing CSV file address lists from any program that will export to CSV. Yet another oldie but a goodie...
Encrypted Address Book v1.3.1.2
LINK: MrsP_Encrypted_Address_Addon_v1.3.1.2-070918
MD5: A5864E4BF02C9E6F4393B862270AA172
SIZE: 275 KB
Description: Simple address book with encryption facilities
Builddate: 2002/09/20
Op System: Windows 2000, XP & 2003 (x86 only)
Language: English
Title: Encrypted Address Book
Version: 1.3.1.2
License: Open Source
Website: http://www.geocities.com/niq.rm/eab/EAB_Frameset.htm
Installs to: "%programfiles%\Security\EABook"
Enjoy (or not)Encrypted Address Book
This is a simple address book with encryption facilities. It makes a shameless copy of the basic functionality the Windows Address Book provides, but uses the Blowfish encryption algorithm to hide the data from prying eyes.
The program can also import data from CSV files. You can use the Export to CSV function from most address book programs to transfer all your data to this format and then import it into the EncryptedAddressBook using a simple wizard.
Encryption is provided through the DCPCrypt components v1.31 by David Barton. Many thanks to him for making the sources publicly available. As far as I am aware, there is no way to recover forgotten passwords, so be very careful about what you choose and how you safeguard it.

[Edit 2006/04/19] Modified install path and added reg entries for file associations
[Edit 2007/09/18] Rebuilt with uninstaller