Where in Ireland are you planning on going? Do you want to rent a house that is located in a small harbor village or close to a bigger city? My personal preference is the Southwest, say on the Dingle Peninsula or a bigger city like Galway. Here are some links I had bookmarked in My Favorite Places that may be helpful to you.
http://www.tourismresources.ie/cht/castles.htm Vacation Castles, Cottages &Country Houses to Rent in Ireland, self catering or staffed http://www.cottagenet.co.uk/index013.htm CottageNet Self-catering Accommodation Ireland
Or just do a search for self catering Ireland and see what you come up with.
Hope this is helpful. Debbie in NC