It is "greener" to repair a historic door or window and retrofit with weather-stripping and storm windows / doors than to replace with new. You may only have to repair 1 or 2 components of the window (most often sill and glazing putty) instead of sending the entire window to the landfill.
Most historic windows and doors were milled from old growth lumber, which is a more durable material than recently milled or engineered new growth lumber components. This means that the window / door that has been around for 100 years can last another 100 years with proper repair and maintenance - you won't find that guarantee on a window or door made of new growth lumber.
Repair and maintenance is much more cost effective and produces a faster return on investment than full scale replacement of materials. Studies have proven that historic windows and doors, when in proper working order and retrofitted with weather-stripping and a storm window / door, provide the same insulation value as a new double pane window.
Weather stripping and a storm window/door is almost always less expensive than a brand new window, therefore increasing the return on your investment. Storm windows/doors and weather-stripping usually pay for themselves in energy savings after about 5 years, the same cannot be said for new windows, which usually take well over 100 years to pay for themselves with energy savings (that is if the new window is still around in 100 years).