To get to the city center from the airport, the fast/cheap way is to get the city center shuttle. Is a green colored bus (two floors) that you can take for 6€ just in the exit of the airport terminal. The last stop is on O'Connel street. From there you are on a walking distance to Isaacs and Jurys Inn.
To get to O'Callaghan from O'Connel I would take a taxi if you don't want to be carrying bags during a 15 minutes walk.
A Taxi from the airport to the city center is around 25€, so I recommend the Bus for those who go to the city center as it is almost as fast as the taxi itself.
East Point (Sun Offices)
To get to east point, the easiest way is to get the train (DART), the stop you are looking for is Clontarf Station, choose this destination when buying the tickets in the machines.
From Jurys Inn and Isaacs you should take the DART from Connolly Station. From O'Callaghan Alexander you should take the DART from Pearse.
You have to take the lines that goes to Howth or Malahide. In case of doubt, ask in the information desk about which platfrom should you take.
In the Clontarf station, there is a free shuttle bus that takes you to the East Point Business Park,