You don't need a visa if you're from Canada or United States.
True, you don't need to do anything before you get here. BUT you will need to have certain documents in your hand (read in your hand luggage) when you arrive at customs.
"You should have all documentation relating to your studies on your person when coming through immigration. In other words, you should have your letter of offer of a place at the school, or educational institution ready for inspection at immigration. You can read more in our document on
permission to land in Ireland."
It is not unheard of for the Customs Officers to also bother people from countries that don't need to have a visa to study in Ireland for the other documents that you would need to send in with a student visa application. Though they likely won't ask for any of these, if you would like to ensure that no matter what happens you'll get through customs popping a copy of the following into your hand baggage might be a good idea:
Letter of acceptance from a recognised school/college/university in Ireland confirming that you have been accepted on a course of study. This course of study must be full-time (lasting an academic year) and have a minimum of 15 hours per week study time.
Evidence of your academic ability to pursue the chosen course through the English language (unless it is an English language course).
Evidence that the fees for the course have been paid in full.
Evidence that you have enough funds (€7,000) to maintain yourself for the initial part of your stay.
Evidence that you or a sponsor have access to
at least €7,000 for each subsequent year of your studies, in addition to the course fees for each of those years.
Evidence that you have private medical insurance
An explanation of any gaps in your educational history
Confirmation that you intend to return to your country of permanent residence when you leave Ireland
Visa Details:
http://www.citizensinformation.ie/categories/travel-and-recreation/travel-to-ireland/student_visas
AND when you are in Ireland, each year you will need to register with the Guards (police). It costs 150euro and, in Dublin at least, is a real pain. Wherever you are don't leave registering to the last week you're allowed.
Registration Details:
http://www.citizensinformation.ie/c.../registration-of-non-eea-nationals-in-irelandhttp://www.citizensinformation.ie/categories/travel-and-recreation/travel-to-ireland/student_visas