Update from 2021: just use MathJax; you shouldn't be supporting old versions of IE any more.
I want to use MathJax to display MathML equations, but its performance in IE is unacceptably slow (yes, I read about using EmulateIE7, this is also unacceptable as it would break other areas of the site).
I don't need to support user-generated equations, and most of my data is already in XML form, so doing an XSL transform to HTML seems like the most compatible solution.
Ideally, the HTML would be similar/exactly the same as that which comes from MathJax. Displaying an image in place of the whole equation is a poor solution, as is requiring IE users to install MathPlayer.