Unless the person has never had a computer or does not know where they can get a used one the new ones are not going to off set the energy of disposal of the old one and creation of the new one. I believe that this applies to just about any commodity.
To be really green I think that they should take in the {insert thing name here} for disposal / recycle, and show the true cost like a sticker on a hot water heater shows the energy usage.
People are way too busy patting themselves on the back driving their Prius and using their green MacBook when the landfills are full of their old SUV and Gateway notebooks.