title: How does one modify an old school NES game?
body: <p>I sometimes see modified NES games, and I'd like to try my hand. What tools are used to accomplish this?  Is there some magic repository of source code sitting around somewhere that I don't know about?  My question is, what is step one to modifying any arbitrary NES game?  (If step one is something like 'get your head on straight', then please give me steps one through three.)</p>
  
  <p>Thank you</p>