Eiffle, 

The people at the school where you are interning should have some recommendations and help for you. Trinity College lets (rents) dorm rooms during the summer. Here are a few other self-catering rentals:

http://www.embassycottage.com/

http://www.molesworthcourt.ie/

http://www.self-cater.com/

http://www.ocallaghanhotels.com/Apartments.aspx

http://www.ellisapartments.com/

http://www.augustineapartments.com/index.php

http://www.yourhomefromhome.com/

Always contact the place you are interested in to ask questions about booking, length of rental, etc. Most places are flexible if you tell them what you need.

I hope you find just what you are looking for. We would love to hear back from you about your experiences in Dublin.

Michele