Need a javascript guru for this one.

Hi. Sorry, missed your later replies. Now i see you have disabled the parallax.
As said, this should work (for a plain direct usage):

var windowWidth = screen.width;

Then, to make it dynamic (to allow browser rescaling) you should use window object resize (jquery):

$(window).resize(function() {
    windowWidth = screen.width;
});

This is a quick workaround, but again, it should work.