Hi Steve. Quite a broad topic when you start thinking about it - fly from where? Fly to Dublin. Where to stay? What to see and do over 3 days.
You can fly Ryanair from Carcassonne. It is often worth checking out what Aer Lingus will charge from Toulouse or Perpignan. Depending on flight times, how much time will you actually have in Dublin? Where will you stay? City centre or suburbs. What to see? Big question - for example, is it the Book of Kells or the Jameson Whiskey factory or indeed the Guinness factory. All charge an entrance fee but lots of other places are free.
Do you want to stay in Temple Bar area? Lots of craic and music, lots of pubs and very noisy at the weekend, or are you a more sedate, sober person? Be careful of some hotels out in the suburbs offering cheap rates - you will then find that you are miles from anywhere and will either have to hire a car or spend a fortune on taxis. Like any other capital city, there are areas where you should not go, or be very careful with wallet well tucked away.
There are (well there were befor I left Dublin over a year ago), some interesting pub crawls - there's a literary pub crawl, and I think there was a vampire or haunted house pub crawl. You will want strength and stamina for this!!
If any of our Irish writers are of interest - there are lots of opportunities such as the new Bram Stoker visitor centre (some people are surprised to discover that the author of "Dracula" was Irish). You can check out in advance what plays are on in the Abbey.
If on the other hand, you just want to treat yourself and your mate to a "piss-up" weekend, then you should research hotel in Temple Bar and other areas in Dublin 2 and 4. Dublin is divided by the river Liffey, and the postcodes are even on the south side and odd on the north side. So look out for hotels with Dublin 2 or 4 as their address. I wouldn't recommend anything with a Dublin 1 address - parts of Dublin 1 can be a bit rough.
If there's anything else I can help with, just ask. My OH, Henry, is quite well informed on many aspects of Dublin's history.
Oh, and come and visit us when you are settled in Trebes. As I think I mentioned to you months back, we are in Lagrasse which is about 0 - 40 mins drive.