The first link is something along the lines of my idea.. Its actually pretty cool to see someone else has already done it.... Around 2:45 in the first video you get an idea of the alternator application...

http://www.youtube.com/watch?v=eknnz...eature=related

Second and third link are just a couple examples that a peddle bike can power an alternator.

http://www.youtube.com/watch?v=kVAZIDFMRXY

http://www.youtube.com/watch?v=T3JPZ...eature=related

I'm not sure where you got the idea that you need a gas engine to spin an alternator. What you need with an alternator is an initial charge make the alternator produce electricity.. which is fairly easy to come by since its connected to a battery... You can actually use an alternator in a wind turbine setup as well, provided you have enough wind to spin at the required RPMs...