dwditty,
I highly recommend the cassette tape series "Learn to Sing Harmony" taught by Cathy Fink, Marcy Marxer, and Robin and Linda Williams. It is available through Homespun Tapes, 1-800-33-TAPES. Costs $37.50 US Dollars. They review the basic theory of harmony and take you through many examples giving you opportunities to sing along with a harmony part and then to try it on your own with the lead part.
In my search for better harmony singing I found this tape series invaluable. All four people have a love for traditional and country music and all the songs were familiar to me.
Enjoy the music!
Roger in Baltimore