Listening to Seamus' own version goes along way to giving you a good feel for the Irish pronunciation.

My advice is to listen to the song over and over to get a good feel for the lyrics BEFORE reading the phonetic. Even try to sing along to what your ear picks up. This (I think) is the best way to get the real sound or flavor of the words. Naturally we will not be able to get all the sounds right at first but then that is when you use the phonetic to correct your little mistakes or fill in the gaps.