I suspect that the image resizer script works via a standard window.onload type of call? How about replacing that call with Prototype's dom:loaded?
The advantage of this is that it is triggered while all content is loaded, but before images are rendered. I've used this successfully on a site of mine, it works well. This will likely result in faster page renders on threads that have large images that mess up the layout initially.
It should be easy to modify the call, you would just need to load the Prototype libraries and then replace your onload with the dom:loaded call.