If they had a full nuclear weapon they would have detonated it by now. In terms of dirty bomb(s) that is far more easily obtained and detonated. However, Al Queda and other terrorists want BIG televised explosions on multiple targets which drive new recruits. That is the sole reason I believe we have not been attacked by dirty bombs.
i dont take much comfort in the whole if they had them, they wouldve been used already however on the bright side it is the general consensous (if they do indeed have them) that the weapons would most likely not work as intended if at all.