Hi Stonejohn,
I recommend that you get yourself a book on the subject. One I can reccomend is Sara McQuaid's THE IRISH DADGAG GUITAR BOOK, on OSSIAN Publications, ISBN 0 946005 931.
She gives a very good explanation of how the chords are built. I mean, even I understood it!
Give it a try, it's a very good book, and it also features a lot of other information that is handy to a guitarplayer.
Magpie