Go to the Admin section of your blog, and in the “Custom CSS Selectors” textbox add:

main {
margin-left:200px;
padding:0px 20px 0px 0px;
width: 580px;
}

It still has a bit of gap-osis, but at least your main content will end up where it does for IE. I haven't tried this out on Opera yet, but I've implemented it here and there.