Nice discussion at Unclutter about minimalist software options for focusing on writing (including a comment that points to DarkRoom, the Windows equivalent of the ultra-popular WriteRoom).
One way to achieve zen word processing is to hide the fact that your modern computer is a modern computer. (Out there, no doubt, is someone who paid $1,800 for a MacBook Air only to then run WriteRoom on it.) It's an attempt to travel back to a time before virtual tailfins. Another way to zen, however, is to simply use the tools from that era--the era in which word processing had been perfected.
This gets into the discovery of the Alphasmart Neo. Very cool. For about $200, you've got almost unlimited battery life, super lightweight, and nothing but word processing. This might need to go one some kind of birthday wishlist as I continue to work, behind the scenes, on finishing my leukemia story. What a great way to just write.