CSS and tables is murder on performance. Especially when your CSS is the crummy IE-friendly kind.

I advise using proper more targeted CSS selectors, seeing if the board can output non-table layout code and adding in the /IE7/ script.
I've had stunning success with this javascript "suite" all the way down to IE5.5....

The way most people have gotten themselves into using CSS these days (due to IE), you can totally see why the browser would croak on all the instructions. I cringe thinking of the thread graph*...

* Were you able to make one