[XeTeX] using cm math symbols with xetex

[Friedman, Joshua]

Hello,
I just discovered XeTex. I have it working for non-math text, but for math text I am having a little trouble. For example, things like square roots work, but something like \sum_{n=1}^j doesn't typeset.  Also, things like
\epsilon, and \pi don't seem to work.

Does anyone of a sample math-filled file (with the proper headers) that works. If so, could you please email it to me.
Thanks
Josh