There are many sources of information on creating address-family independent applications. One of my favorite books is Unix Network Programming, Volume 1, Third Edition, Addison-Wesley, W. Richard Stevens, Bill Fenner and Andrew M. Rudoff, 2004, ISBN-10: 0131411551. This book has a web page dedicated to it where you can download the code examples and experiment yourself. Other books you may want to check out are the book TCP/IP Sockets in C, Second Edition: Practical Guide for Programmers (The Morgan Kaufmann Practical Guides Series), by Michael J. Donahoo and Kenneth L. Calvert, 2009, ISBN-10: 0123745403. These authors also have an earlier book TCP/IP Sockets in C#: Practical Guide for Programmers (The Practical Guides), by David Makofske, Michael J. Donahoo, and Kenneth L. Calvert, 2004, ISBN-10: 0124660517. If you write code in Java you should check out these same author's book TCP/IP Sockets in Java: Practical Guide for Programmers, 2nd Edition, Morgan Kaufmann, by Kenneth L. Calvert and Michael J. Donahoo, 2008, ISBN-10: 0123742552. Another useful book is IPv6 Network Programming, First Edition, Digital Press, by Jun-ichiro itojun Hagino, 2004 ISBN: 1555583180.
There are also numerous resources available on the Internet. As they say, "If you haven't Googled it, you haven't looked!" Owen Delong's of Hurricane Electric has a web page that contains useful information. Derek Morr of Penn State has a nice page on IPv6 Programming. Eva M. Castro also has a useful page on how to port applications to IPv6.
No matter where you start learning about how to create address-family independent applications, the important part is that you start working on this now. That way you will have longer to perform the conversion and have more time to be relaxed and thoroughly test your applications.
Scott