Hi,
Well, one great thing in your favor is that you are trained in an area (nursing) that the Irish government has deemed particularly understaffed over here.
If you check out the Irish nursing board at
www.nursingboard.ie & click on 'Registration' on the left hand side. This will take you a page with info for non-EU people. See the first link for Applying for Registration in Ireland for Overseas qualified Nurses & Midwives. Also, at the top of the screen you will see links for a Working Visa/Work Authorisation leaflet. I'm sure you can contact the Nursing Board directly with your queries as well and talk about your particular situation.
Additional information for work authorisations can be found on the Department of Enterprise, Trade & Employment website
www.entemp.ie and citizenship details (incl. for those who are married to an Irish national) can be found on Dept. of Justice
www.justice.ie
There have been talks of Green cards for specially trained people such as yourself but nothing has been put into law as of yet, so I would assume that right now, a Work Authorisation (as you are from the States) would be your option.
Good luck!
Maria