The government of Northern Ireland has officially confirmed that it lobbied HBO for them to film A Game of Thrones in the country. Previous reports about the filming location had merely mentioned 'Ireland', leading many fans and commentators to assume the show would be made in the Republic, which has already seen many major film and TV productions filmed there including the likes of Braveheart and The Tudors. According to the report, the Northern Ireland First Minister and Deputy First Minister spoke to HBO representatives in LA last month to secure locations in Northern Ireland, with the massive Paint Hall Studios in Belfast playing host to interior filming. A Game of Thrones will become the biggest television project to ever be filmed in the province according to this BBC piece on the project.
This news comes shortly after strong rumours started circulating that there will be additional filming in Morocco and Scotland, and that casting has already gotten underway behind firmly closed doors. The pilot will start filming in October 2009. The earliest possible air date for the series I would estimate to be late 2010, but 2011 is far more realistic at the moment.
Word from GRRM here and some more local reaction here.