In general CEPT arrangements ONLY apply to the “top” class of licence from each country - Known as Advanced or Full in some countries, Extra in the States etc. etc.
There is however in addition to the CEPT TR/61-01 agreement an EU agreement (ECC recomendation (05/06)) that allows the midde class (Intermediate, Standard, Novice) licence to operate with the equivalent level of rights to the middle licence in the other country as long as the syllabus for this level of licence conforms to the European standard (see ERC report 32 from September 2005). Far fewer countries have signed up to this agreement, and as far as I know, this is only within Europe at the moment. Ireland is not a member of this agreement (I believe Ireland only has one level of licence - full). The US is not a member of this agrement.
So if you do not have the top level licence in the US, you will not be able to take advantage of the “easy” reciprocal process and will need to contact the Irish authorities directly to see if they are willing to issue you a one-off reciprocal licence for the period of your stay.
By the way, I presume you are reffering to southern Ireland not northern Ireland. If the latter, you will need to aproach the UK authorities for the same reasons.
I hope this helps, 73 Ed.