Played around (quite a bit) with Lindquists brownian motion code. Here's what I came up with. Tried to play with making the space where the squares aren't the focus. Anyhow, here you go:
[swf=http://www.picrack.com/001/other(3)/blocky1.swf] height=125 width=550[/swf]
EDIT: Added preview.
EDIT: Updated with slightly smoother movement.