@Jimis your blocks are mostly ok, you are adding item "1" to the list, you only forgot to store the new list via StoreProperty method again, so later you see the difference after button click in the user interface... don't forget to open the listview there
Also there is no user interface in the background
EDIT: what you are doing is no real background processing, you are only creating the process, so this is not really a test if something is working in the background or not...
Taifun