Columns order in a XUL tree

Hello All,

I've a xul tree where some columns are defined into a .xul file and some 
are dinamically created at run-time.

Once all the columns are added to the tree, I need to change their 
displayed order.

I tried to modify the ordinal* attribute but I can't make it to work.

Which one would be best method to do it?

Many thanks in advance,
Guido.

(*) https://developer.mozilla.org/en/XUL/Attribute/ordinal