I don't think it's the image that's actually causing the issue (EDIT: Assuming that by "image" you mean the big yellow Windows' Dev Centre one), as it appears on pages without the issue too (see screenshot), although it does make it obvious - most stuff below the top menu bar seems to be left aligned. I did try tweaking the width of .mainHolder but it's so zoom/window size/screen res dependant it's not really worth it (fwiw 67.5% seemed about right for Firefox 11.0 at 100% zoom on my 1440*900 laptop screen).
EDIT: Excessively zoomed for clarity
