How to get to Dublin
Dublin airport is serviced by most large airlines, however excellent deals can be found using Ryanair and Aer Lingus, the two main Irish carriers, especially if you book well in advance. Two brilliant flight search engines that might help you plan your trip are Skyscanner and Hipmunk.
There are also many ferries from the UK, France and Holland to Ireland. Check this site out for more info: http://www.ferry.ie.
How to get from the airport to Dublin city centre
There are many options to get to the city from the airport. A taxi ride from the airport to Trinity College near Grafton Street in downtown Dublin costs approximately 30 Euros with a driving time of approximately 20 – 30 minutes, depending on the time of day and traffic. A less expensive option is by bus/coach. Close to the exit near the baggage claim area of the airport you will find the large blue Air Coach buses. For the price of €7/8 Euros single, or €12 Euros return you can have a fairly easy ride into town with your luggage stowed beneath the bus. Ask the driver which one is best for Trinity College (which is close to both hostels). The last option is the public bus which is very cheap but takes a very long time and covers a lot of suburban Dublin before reaching the city centre.
How to get around Dublin
Dublin is pretty small. The city centre is easy to get around by foot but should you want to go further the DART (green train serving suburban Dublin along the coast), the Luas (inner city & suburban tram network) and Dublin Bus (city and suburbs) are pretty easy to navigate around.
How to get around Ireland
The easiest way to get a round Ireland is by train. It’s not too expensive (cheaper if you book online and in advance) and is pretty fast. Check out the website here: http://www.irishrail.ie. Rural buses are cheaper but take quite a long time – www.buseireann.com. But you can also get direct buses for quite cheap. There’s a variety of them – Go Bus, Aircoach & Citylink.
Finally, renting a car often makes everything easier. Details here: http://www.irelandcarhire.com.