Typically, that absolute positioned image would be positioned into place instead of margined.
I also think it should relative to #container and that #bg-pic-div is not needed at all.
As for your x scrollbar, your site is much wider than your 960px wide container now. The browser has to deal with the overflow somehow
...have you tried overflow: hidden; on the body of the document? That's probably not going to work too well on smaller screens though.
Have you looked for a js solution yet?