If you are looking for a good metric for an enviro friendly laptop, I recommend looking at battery life. This will encourage you to buy a less powerful processor, (which is rarely needed) and pay less for a laptop that will last longer without being plugged in. For most of us, computers are massively over-engineered for our needs, and use more energy as a result. (If you edit video, then maybe you should look at a desktop.)
Personally I own a 2000 apple ibook, and if I was looking to buy now, I would recommend waiting for the upcoming ibook replacements from Apple/intel as an inexpensive, low power machine that will last a few years. If you must buy windows then look for a laptop that can take additional RAM memory (1-2GB ceiling), as this RAM Ceiling is quite likely to be the constraint that makes your laptop obsolete in the future, especially with a new version of Windows out next year.
My 2c.
Ian.

I've heard from numerous electrical engineers (my husband is one of them) that powering on and off electronics wears out the components....kinda like a light bulb. They never pop when the lights on. They always pop when you first turn on the light. Anyways, so it's always been recommended to me to use the sleep feature on the computer....don't shut it down unless you're not using it for days at a time or you're going out of town. I think this would make more sense then always shutting it off since the shut down wears out the components and then you'd have to buy a new one sooner and create more toxic waste. Anyone heard anything similiar?