just seen this on digital spy. explains things fairly clearly.
http://www.digitalspy.co.uk/digitaltv/a117906/ireland-confirms-national-dtt-rollout.html
Ireland confirms national DTT rollout
Friday, August 1 2008, 11:55 BST
By James Welsh, International Editor
The Republic of Ireland will launch a national digital terrestrial television system by Autumn 2009.
Digital terrestrial trials, which were conducted by a stakeholder group including BT, RTÉ and Sky among 500 households in Dublin and Louth, ended today. The test service carried 17 television channels, 16 radio services, a high definition service, an electronic programme guide, and a digital teletext system, in the same amount of spectrum used to transmit four analogue services.
The Irish DTT service will use the more efficient MPEG-4 compression standard from launch, rendering set top boxes and integrated digital television sets designed to work with the UK's system - which at present uses MPEG-2 - incompatible. However, UK communications regulator Ofcom plans to transition one multiplex to MPEG-4 next year.
"MPEG-4 is the technology of choice for DTT as it allows space for more content and for high definition channels," explained RTÉ director general Cathal Goan. "We want to ensure that our viewers get the best value for money in the switch to digital television – more channels, more services and better quality pictures."
Communications minister Eamon Ryan said that the Irish government would commence a public information campaign about digital terrestrial television next March.
"Central to the success of national rollout will be a public information campaign... explaining digital television to the nation," he explained. "My Department will begin this national information campaign in March 2009, in advance of the autumn 2009 launch date. Analogue switch-off must be complete by 2012.
"We have a tight timeframe but I am confident that with all players working together and with public buy-in that digital television in Ireland will offer new and exciting content and technology to the Irish viewer."
Once built, Boxer DTT will operate a subscription service on the platform to be available in addition to an RTÉ-run free channel bouquet.