To help prevent any squeaking when sliding a window sash, I recommend rubbing a little wax on the jamb. What did you think I was talking about? I've used Gulf Wax with great results, and it's edible just in case the kids decide to lick the window jambs. Just cut off a chunk and slide it along the jamb. Repeat as often as necessary. It works great on old style kitchen drawers too, the kind where the drawer just slides on wooden runners.