Help with getWidth()

Helpless newbie here. I am trying to open a new window, sized appropriately to hold either a portrait or landscape oriented image. For this I need to know the width of the new image before I open the window.

I'm pretty clueless, but this seemed to me to be the simplest way to do this:

var img = new Image("http://helma.org/images/hop.gif");
var w = img.getWidth();
newwindow=window.open('','jav','width=w,height=100 ");

Opening the window is no problem, but getting the width of the image is. Any help? I'm trying to keep this simple. Do I have to load the image first? If so how? Do I need to create a class? If so, I am clueless. I have searched out a million references to the getWidth() function but there are no simple examples of this use.

Does that help at all?

Um, ignore the spaces in myImage.width.toString()