Hi Ekenryd, also see this other recent thread for some more discussion on the variety of options for selecting an obscured object:

http://moi3d.com/forum/index.php?webtag=MOI&msg=3324.1

There's also a video there that shows how window selection works - like Burr mentions though it's pretty straightforward - you just click in an empty area and hold down and drag the mouse.

That window selection method can be useful for selecting a batch of objects instead of only click on them one-by-one and it also works for grabbing obscured objects as well.

- Michael