Human power is actually pretty pathetic, an average person can put out only a couple hundred watts for a few hours, so you would have to work pretty hard just to run the computer you're reading this on, see;
http://www.ent.ohiou.edu/~et181/hpv/hpv.html
If you're Lance, you can increase that a few times. For survival/eco-friendly power, wind, solar and hydro may be a better choice:
http://www.otherpower.com/

As far as converting a bike into a moped, i've seen products that do this, but only gets speeds up to 30 mph. Besides, i've taken spills on my bike at 20 mph while commuting and that's no fun, can't imagine doing it at 30+ mph.