Ford suggests using DOS to get back to basics and unplug, but you can do it with less pain by just buying an old Mac dedicated for writing work. I use an old powerbook that doesn't have games and is too slow to connect to the internet. Using DOS hurts my head.

I have great willpower, but less so when I write. You'd be surprised how productive you can be by not being in the same room as a computer internet-ready (or if you only have one room, turn the thing off). It helps.