hi,
i have a table of places that looks like this:
-place
-parent place

i want to modify ajax combox to have a possibility to
select
>in the beginning from places without parent
>go to the bottom in nested records,
>choose the last nested record

could you provide me some guidelines?

Is it a 'nest' table design ?

I mean, will your program treat 'places' table as a hierarchical table ? (Not possible yet in cook, but coming)
Because if you plan then to have such structure, then the code must be coded in a recursive way.

MODEL
prepareQuery():
Invent a new state name for this query wich will sort the rooted places first

VIEW
The combo boxes are filled in the view file.
Open the view file corresponding to the layout you want and complete / modify the code there.
All you have to do is
model->setState('myNewInventedState', true);

HTML
If you want to group datas in the combo, then you can do it easily with JDom ('groupby' property)
You can eventualy do this before in the builder (Group By : [FK] parent place > title )

Hope it helps.