[XeTeX] Stuborn math fonts

[Juan Acevedo]

Hello

I have not been able to find a solution in the archive for my problem  
with the following minimal file:
----------------
%!TEX TS-program = xelatex
%!TEX encoding = UTF-8 Unicode

\documentclass{book}
\usepackage[no-math]{fontspec}
\setmainfont{TeX Gyre Termes}
	
\begin{document}

Hola

$\overbrace{para\quad probar\quad esto}$

${para\quad probar\quad esto} $

Chao

\end{document}
----------------

where I keep getting CM fonts in math mode, instead of the Termes I  
need. I have tried also putting the \setmainfont command after  
\begin{document}, but the result is the same.

I just just installed MacTeX-2008 (running smoothly and quicker! with  
big thanks), i.e. I am using
XeTeXk, Version 3.1415926-2.2-0.999.6 (Web2C 7.5.7)
and the latest (I suppose) xdvipdfmx.

Please, any help will be much appreciated.

Thanks in advance,

Juan