cant think of a way to solve your problem, other than making your background image complete (don't cut it off at the bottom). Really nice design by the way.
got something to add, just had a look at the entire background image. I hadnt realized it was one entire picture for the background, not a good idea. 1,512px × 800px what kind of screensize is that??? I can't even see the right side on my feeble 1024*768 monitor (thats a realy shame). First separate the image in to two parts. Get rid of the big blue middle part with no information on it. Set you background color to that blue. Set the background image to the left part of your splitted image. Add <div style="float:right;width:200px;height:300px;paddin g:10px;background:red url('bla.jpg');">XXX</div> or something similar to float the right half. This might cause problems with the z-index. You could also just forget about the right half... or fix your sites width to work on 1024*768 (what I personally don't think is a good idea).