He's in love with the idea of writing a game. He might not actually like programming.<p>So, you need to start with something simple that will get him immediate results.  Which really means HTML these days as everything else needs umpteen objects before you can see any results.<p>If he takes to it, you can then move to CSS and javascript. And if you get this far then the leap to actionscript or python or whatever isn't that big and you'll know that you have a good student,