And if you want to know more in general about electrics for aviation then read this:

http://www.oz********.com/2007/01/el...ic-flight.html

These are the questions you need to answer:
1. What's the approximate AUW of my aircraft?
2. What type of aircraft is it? (determines how much power you need per pound, as well as what sort of motor speed you want - high speed model - smaller prop with faster spinning engine, 3d plane - larger prop with slower spinning engine etc).
3. Choose a battery and motor together (normally best) or choose a motor that works with your existing fleet of batteries (cheaper). The number of cells in the battery will dictate the voltage and hence how fast the motor spins, which when coupled with a prop determines how many amps the motor draws, which when multiplied by the voltage gives you total watts.

It sounds confusing (and no doubt my explanation hasn't helped), but it makes sense once you've tried it once or twice. The important thing is understanding that the prop, motor and battery are all interelated and the choice of any one of these affects your choice of the other two.

Cheers,
Oz.