Help With Snow Tut. AS

Could someone PLEASE help me script the snow to my dimensions:
Stage 600 wide x 400 High
I only want the snow in an area 432 Wide x 296 High at the X=80 y=52 position
I’ve tried scripting it and totally messed it up…again & again & again. I’ll never learn this stuff :<(
Here’s the original script:
onClipEvent (load) {
onClipEvent (load) {
//specifies the size of the movie stage
movieWidth = 300;
movieHeight = 200;

//variables that will modify the falling snow
i = 1+Math.random()*2;
k = -Math.PI+Math.random()*Math.PI;

//giving each snowflake unique characteristics
this._xscale = this._yscale=50+Math.random()*100;
this._alpha = 75+Math.random()*100;
this._x = -10+Math.random()*movieWidth;
this._y = -10+Math.random()*movieHeight;

}
onClipEvent (enterFrame) {
//putting it all together
rad += (k/180)*Math.PI;
this._x -= Math.cos(rad);
this._y += i;
if (this._y>=movieHeight) {
this._y = -5;
}
if ((this._x>=movieWidth) || (this._x<=0)) {
this._x = -10+Math.random()*movieWidth;
this._y = -5;
}
}