wow this thread is dense with information.

Because I am intellectually lazy, I have used Murray's method for many years...it works great with a couple of caveats.

...they're not all in Em...listen for the note the tune ends on and thats probably the chord.

...but assuming Em, learn a bunch of inversions of Em and D up the neck, and in approved Celtic style you use as many open strings as possible.

...and finally, use a quick transitional B7 between the D and the return to Em, it will get you free beer.

oh, and get handy with a capo, especially in dadgad.