You need to get out of the spans and in-line styles. They just get things all munged up in responsive. You're telling the system to make this image 2888 wide and it is by Jimminy gonna do it.

Get the width and height out of the in-line and add
Code:
div#bannerOne {width: 100%;}
to the end of your stylesheet.css. You will need to adjust the margin-top in the same listing to something like 35px and it may need to go in the responsive_default.css in order to not mess with the desktop version.

You can decide what to do with the padding on line 43 of the stylesheet.css.