Hi litledeby21
You have heard correctly. Christmas in Ireland is very much a family time and most restaurants/shops etc will close early on Christmas Eve and a few will re-open on the 26th but most on the 27th December. On Christmas day itself there will be very little open, generally only petrol stations and some local spar/centra type shops (think 7/11).
However, with a little planning you can make this a very special visit to Dublin. There is nothing quite like the atmosphere in Dublin City on Christmas Eve - from early morning there will be people rushing around getting last minute gifts, meeting friends for a Christmas drink in pubs and meeting up for lunch. It's a truly magical time in the City and one which many visitors will never experience.
Some things that you need to think of - Where are you staying? Are you within walking distance of the City Centre? Are you self-catering or staying in a hotel? If you are staying in a hotel check if they are open for Christmas dinner for residents. If you are self-catering you will need to stock up with supplies on arrival on the 24th.
On Christmas day you could take some time to walk around the city, see some open air sights and enjoy having it almost to yourself. Even if you're not religious you might like to pop into one of the churches and enjoy a Christmas Mass - just to soak up the atmosphere and listen to the choirs. If you are staying in the city centre you could use one of the Dublin Bikes and take a ride through the Phoenix Park.
On the 26th some museums and shops will open but it is generally another quiet family day. Last year we popped into the Museum at Collins Barracks for an hour and had the whole place to ourselves.
My advice to you is to check out the situation re your accommodation and dining options and once you have the practical things sorted just enjoy the wonderful atmosphere of Dublin at Christmas.
If you have any other questions please post.