Selecting item with another béhaviour

[edipreto skynet be]

Sorry for the break in the thread, but I didn't write this mail on my linuxbox.
What I want to do with my GtkListStore is not configure it to be able to select more than one item. I've already post or read a mail about that. What I want to do is to modify the behaviour to select another item in my GtkListStore.
 
So, I must connect my own function on my GtkTreeView. And this function contain the following algorithm :
 
on_click(item) {
 if (is_selected(item) == TRUE)
  {
    set_selected(item, FALSE);
  }
 else 
  {
    set_selected(item, TRUE);
  }
}

The problem is that I don't know the name of the event, and I don't know how to change the state of an item (selected or not selected).
 
Regards,
 
Manu