Afghanistan is in the process of writing its constitution, and it is not easy. There are 502 delegates, consisting of Tajiks, Uzbeks, Pashtuns and many other ethnic groups involved in deciding many issues including which language the national anthem will be sung. Another issue that the opposition of Hamid Karzai does not like is a strong presidency.
Meeting the Tajiks' demands would be a considerable compromise for Karzai, who has held out for a strong presidential system. His opponents want parliamentary control of the printing of money, the creation of a constitutional court, three vice presidents rather than one, a ban on top officials holding dual citizenship or having a foreign spouse, more power devolved to provincial councils, and for Uzbek and Turkmen language rights in their ethnic regions.
The Loya Jirga was halted after many delegates boycotted the sessions. It is to resume soon and Afghanistan may have a constitution. Now I am sure, we will see the same issues, when Iraq starts writing a constitution.