Fine tuning Snow fall

right now I have a particle engine that creates snow falling. It uses the whole stage (_root). I'm trying to get snow to fall in a specific movie clip so it only attaches, and removes the snowflake (particle) in a selected movieclip. I have a MC called widescreen_mc and inside that I have sky_mc. I would like the snow to fall in the sky_mc so you only see the snow in the screen. I've tried attaching it in the sky MC and then change the other stettings (width height) to adjust, but nothing I do works as expected. Here is the Prticle engine code i've been using. can anyone show/tell me the changes I need to make to get it to work (brief explanation of any code changes would be apprciated so I can see my mistkes.)

Merry Christmas

import mx.transitions.Tween;

import mx.transitions.easing.*;

timer = 0;

timermax = 10;

particleCount = 0;

gravity = .01;

changeOver = 100;

checker = true;

percipitation = function()

{

  //this._x += -5;

  this.yspeed += gravity;

  this._y += this.yspeed;

  if (this._y > (Stage.height))

  {

  this.removeMovieClip();

  }

}

onEnterFrame = function ()

{

  timer ++;

  if (timer == timermax)

  {

  //generate particle

  particle = _root.attachMovie("Snow","P_"+ particleCount, _root.getNextHighestDepth());

  ///needs to set random position across

  particle._x = Math.floor(Math.random()*(1+Stage.width+3)) -3;

  //particle._x = _xmouse;

  particle._y = -10;

  particle.xspeed = random (6) - 3;

  particle.yspeed = random (6) - 0;

  particle.thesize = random (100) + 10;

  particle.fade = Math.floor(Math.random()*(1+50-10))+10;

  particle._xscale = particle._yscale = particle.thesize

  particle._alpha = particle.fade

  particle.onEnterFrame = percipitation;

  timer =0;

  particleCount ++;

  //trace(particleCount);

  clock_mc.swapDepths(particle);

  change_mc.swapDepths(clock_mc);

  winter_mc.swapDepths(change_mc);

  protect_mc.swapDepths(winter_mc);

  holder_mc.swapDepths(protect_mc);

  }

  //}

}