As far as Irish-Catholics supporting Democrats 2 to 1, you are just wrong. Clinton took the Irish-Catholic vote by 16 points in 1996 and Bush narrowly lost the Irish-Catholic vote in 2000. See link. In 2004, look for Bush to take the Irish-Catholic vote outright, as Catholics in general, and Irish-Catholics in particular become more and more Republican in their voting patters.
Whooopdedoo! They voted twice for Reagan!
If you do the least bit of study into political patterns in major cities, you can easily tell where the predominantly Irish neighborhoods are without looking into Census statistics - look for majority white precincts that are carried overwhelmingly by Democrats that have lots of Catholic Churches around. Examples - Grays Ferry and Fishtown/Kensington in Philadelphia, Rockaway Park in New York, South Boston in Boston.
The fact is that most other white ethnic groups, like Poles, Germans, and Italians generally can be found voting at a 6-4 or even 8-5 rate for Republicans, while the Irish are the exact opposite, and the Jews are even further left at about 8-2 Democrat.
BTW, here is an article from July of this year by Mark Shields (who is about as liberal as they come) which makes the same point with regard to Catholics in general --
Long gone are elections like the Democratic victories of 1960 and 1964, when three out of four Catholics voted for co-religionist John F Kennedy and then nearly four out of five Catholics backed Baptist Lyndon B Johnson.
I would be very interested to see something other than an opinion from you that supports your statement that Irish-Catholics vote 2 to 1 in favor of Democrats. I am quite sure that isn't true, but please feel free to prove me wrong.