I experimented with using table-layout: auto, but the way the HTML is designed, the header and pager can't be resized with the grid. As Tony said, there is also a lot of CSS and inline style that are meant for fixed-width columns that you have to combat to try auto sizing.
It's going to take an HTML/CSS redesign to be able to do either auto or fixed. As far as HTML, the main point would be to wrap the header, grid, and pager in a table element. That would make the header and pager automatically size up to the grid size (since it's a div element), provided the width styling is left off those elements. Tables are annoying to work with, but are still the most straightforward way to do that.
The auto-sized grid could disable the drag handles and resizing in the first iteration. However, there could be a case for doing resizing on an auto-sized table. This could be accomplished by using the .offsetHeight and .offsetWidth javascript properties. These properties apparently work in all modern browsers. I tested them to work on at least DIV and TD elements in Chrome, Firefox 3, and IE 7.
I think there is some combination of HTML that could be used both ways, for auto and fixed sizing. The fixed sizing should just require extra CSS.
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