so what happens is, i installed mate desktop, and mate was always on the bottom of the list so i change xwmconfig to make it be in the first ones along with kde gnome and xfce.
the problem is, while i was looking at the script i saw that the preselect item is established by root, so i change it so when a user pick a desktop enviroment the next time he/she run the script the preselected item is gonna be the one that he chose.
if anyone wanna try it out:
https://dl.dropboxusercontent.com/u/33305929/xwmconfig