Problem with Scroller AS, please help!

programming flash
1 
panel.onRollOver = panelOver;

function panelOver() {
	this.onEnterFrame = scrollPanel;
	delete this.onRollOver;
}

var b = stroke.getBounds(_root);

function scrollPanel() {
	if(_ymouse<b.yMin || _ymouse>b.yMax || _xmouse<b.xMin || _xmouse>b.xMax) {
		this.onRollOver = panelOver;
		delete this.onEnterFrame;
	}
	
	
	if(panel._y <= -743.9) {
		panel._y = -743.9;
	}
	
	if(panel._y >= 78.1) {
		panel._y = 78.1;
	}
	
	var ydist = _ymouse - 250;
	
	panel._y += Math.round(-ydist / 7);
}

There is my code from the tutorial on GoToLearn.com on the Scrolling Thumbnail Tutorial. My problem is that I changed it to up up and down now, that works, except when I try to put the code in to stop it from infinity scrolling, it just messes everything up?

	if(panel._y <= -743.9) {
 		panel._y = -743.9;
 	}
 	
 	if(panel._y >= 78.1) {
 		panel._y = 78.1;
 	}

Whats wrong?