Hi,

Assumed there are page items named "box1" and "box 2" anywhere inside mDoc:

mDoc = app.activeDocument;
mDoc.pageItems.item("box1").select();
mDoc.pageItems.item("box2").select(SelectionOptions.ADD_TO);

other select options:

     SelectionOptions.REMOVE_FROM

     SelectionOptions.REPLACE_WITH

use

Adobe InDesign CS5 (7.0) Object Model

or another placed here: http://jongware.mit.edu

rgds

Jarek