I'm sorry folks, but the only way I can see this working including IEs 6 and 7 is using tables.
Working example: Here
The "Greeble" text (I don't really know what a greeble is :) distorts the resizing somewhat, that'll disappear when the columns have background images only.
Issues: The columns need to contain something to be rendered by IE. The
I built in will prevent the complete disappearance of the right and left columns. You will have to find a way around that, maybe with a 1x1 Pixel image or something. You will always have to have some content - even if just 1 pixel wide - in all columns.
Relies on: Tables with an unspecified width rendering the way they do. I think this is pretty reliable, tough.
Tested in: IE 5.5 and greater, Firefox
To anybody who dares downvote this because tables are evil: Find me a better, CSS-based solution that works in IE6 as well, and I will gladly remove mine.
HTML: No separation between markup and CSS, no semantics, just the working prototype.
<body style="margin: 0px">
<table style="width: 100%; height: 100%" border="0"
cellspacing="0" cellpadding="0">
<tr>
<td style="background-color: orange; height: 50%; color: white">
Greeble top left
</td>
<!-- The content area -->
<td style="width: 960px" rowspan="2">
<!-- This is important, serves as min-width replacement. -->
<div style="width: 960px; text-align: center">
I will always be 960 pixels wide
</div>
</td>
<td style="background-color: blue; color: white">
Greeble top right
</td>
</tr>
<tr>
<td style="background-color: blue; height: 50%; color: white">
Greeble bottom left
</td>
<td style="background-color: green; height: 50%; color: white">
Greeble bottom right
</td>
</tr>
</table>
</body>