This is an idea I have been toying with for a couple of months now, but I think a recumbant exercise bike might be a better than a treadmill. My hair-brained scheme is to use the bike to drive a car's alternator (cheap and used), and use that to drive a power inverter & battery. Then use that whole Rube Goldberg contraption to power my laptop. If I get too tired to keep the laptop running, I could switch to AC power. If I find I can't generate enough power to keep the lappy running all day, I could always power the uh... iPod instead? No exercise = no music. I would HOPE I could generate enough power to keep an iPod running.
Green and lean, but mostly... geek.