Some help with coding (flash action script 2.0)

[nacritico]

Well, hellow there. I'm new on this forum, and I was thinking of making some questions.
As you might guess for the title, this are mainly question for someone experimented (or with coding background) at action script 2.0, so probably if you don't know about it, you can't help me here.
Well, the thing is that, as you might know, flash has the option to create classes in order to organize the code. Among the functions I want to give a class, I need to found out wheter my MovieClip is (or not) colliding with other stuff in _root. I already programed the best collition checker my game can have (it register wheter the character is above or below the other movie, I've already tested it).
Now, the problem is that to make it work, I need to make a "for" inside the class code, and for some reason, everything I choose is given back as "undefined".
To make things more clear, here you have the code I'm having problem with:

class player extends MovieClip{
/*
lots of codes that are useless for you
*/
var z
for(z in _root){
trace(z)
//note: this is my problem, z is always "undefined"
if(this.HitTest(z)){
trace("hitted")
//note: so this never happens
}
}

please someone tell me if you know how to fix this ... salu2's

ps: or if at least you know a good page with clear tutorials on how to fix this