Usefull links

http://www.nk2.info/
• NK2.info is a small utility to view and export the contents of an Outlook auto completion file.
• NK2.info can recover e-mail addresses and names from a corrupted NK2 file!
• NK2.info is free

http://www.nirsoft.net/utils/outlook_nk2_autocomplete.html
This utility reads the AutoComplete file of Outlook (with .NK2 extension), displays all email records stored in it, and allows you to easily export these records into text/html/xml file.
It also has an experimental feature to import your outlook addressbook to the nk2 file

http://code.google.com/p/debunk2/
a tool that tries to get info from an existing .nk2 file and can export it to the following formats
• CSV/TSV - comma-, tab-, and semicolon-separated lists
• vCard - virtual business cards (vcf)
• SyncML - an xml dialect of vcard (planned)

http://www.ingressor.com/about_nk2_files.htm
A full-featured NK2 (auto-complete) file editor. Commercial software, pricing starts at $40 to $350