Check out this BBC News Article: http://news.bbc.co.uk/2/hi/middle_east/3153732.stm
Anyway, the US government has hoped to draw up an Iraqi constitution in about six months...however this seems to be unrealistic.
As it says in the article, the US government is unsure wether the delegates on the constitutional convention should be elected or appointed, the latter would be the more difficult and time consuming.
It seems to me that they would HAVE to be elected, as tedious as the preperation for such an election would most likely be. If the US were to appoint members, there would be a inherent bias towards the western way of thinking, which is quite unfair for the people of Iraq.