I've linked over to this blog from my other, more mainstream writing (if you could call it that) and I had more than a few people ask me how to use their computers in a more green fashion, and if it's linked to minimalism at all.
The process is simple.
1) Learn Linux.
2) Use Linux.
3) Stop buying computers. If you need to buy something, buy used and low powered. Aim for laptops.
3.5) If the power usage is too high, replace parts with power saving parts.
4) Turn on the power management in Linux.
5) Get a good power strip that can disconnect all power usage when a switch is flipped. Use it when the computer is off.
Linux helps with this, but the possibilities are enormous in all three operating systems, though not entirely equal. I picked Linux as a special case because its lifespan is not dependant on the growth of software bloat*, but rather the reliability of the hardware it's situated on. Mac OS X could possibly be similar (post their PowerPC swap), but then again, suggesting one buy a new computer for the privilege isn't very green.
This is equally valid for other components as well, such as tablets, MP3 players, cell phones, remote storage, and input devices such as mice, touch pads, and keyboards. Personally, I question the need for buying most of the list entirely for any reason other than replacing a broken and strictly required product, but then again if you tried to take away my Sansa Clip+ away from me I may just strangle you. As usual personal priorities are more of an issue than otherwise.
In any case, it's not a complicated issue.
*The exception to this would be some of the bigger desktop distros like Ubuntu, who seem to have grown quite a bit on the CPU and RAM munchies front (though they do seem to be trying to keep this down in 10.10). However, it's easy to switch to something a bit more judicious in its systems requirement front, such as Debian, or simply switching to a lighter desktop like IceWM or Fluxbox.