Some still use tables for easy vertical and horizontal alignment, but I think with a layout like that you could simply use two divs, first one with the plain white background and a no-repeat background image aligned to the right, and the second one with a border + outline (or border-image, but it works basically in the same way). Basically this idea, more or less:

<style> .bg {background: #FFF url(http://i.imgur.com/mDVNvc0.png) no-repeat right; padding: 5px 190px 5px 5px; min-height: 200px;} .innerBox {background: #040; border: 2px solid #000; outline: 1px solid #000; outline-offset: -4px; padding: 5px; color: #FFF;} </style><div class="bg"><div class="innerBox">

Result. Is it close to what you were looking for? Of course, the specific padding values would need to be adjusted to how far away you want the postbox from the postarea's border, and one of the values would be of the image's width. Colors and the image would be adjusted (along with the class names to make sure it's something unique that won't be used by anyone else), obviously, but the main concept is there.

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Turnips.

background: #000 url(http://i.imgur.com/mKJu4y3.png) no-repeat right top;

The image can be algined to the top, center or the bottom of the post. Second, CSS can't do miracles, empty spaces on the images themsleves are still considered part of the image. To make sure the image is perfectly aligned to the top of the post, the empty space at the top needs to be removed as much as possible.

A few other things: change the "bg" and "innerBox" names to something more descriptive so they don't conflict with anything else that may use such generic names on the future.

In order to make it occupy the entire frame, add a min-height: 350px; to the first element. If it still doesn't occupy the entire frame, just up the value a bit. Don't use a value much higher than you need though.

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Turnips.