The BBC has more details so far than RTE: Irish journalist Rory Carroll, who writes for the Guardian, has been kidnapped in Iraq. As we've noted recently, the Department of Foreign Affairs has various headaches at the moment with citizens in detention in other countries, but this is clearly the most perilous.
The precedents for these cases lead one to believe that (a) he will be freed, hopefully quickly, but that (b) a ransom will be paid, although (c) the government will deny it, most likely via relabelling of fees to "middlemen" or concessions provided by 3rd parties as not counting as a "ransom." This was almost certainly the case for Franco-Belgian hostage Florence Aubenas and the Italian hostages, the two Simonas.
UPDATE: The RTE story is now more elaborate. Rory is the son of the well-known journalist, Joe Carroll. We wish that Foreign Minister Dermot Ahern's statement in the RTE story sounded more pro-active.
MORE LINKS: Jim Romenesko's Media News. RTE story suggesting link to an al-Sadr militia.
FINAL UPDATE: He's freed. That was quick.