Trouble with bounding box in includegraphics for EPS file

Hi,
I have installed MiKTeX 2.9 on my PC under Windows 7.
I want to include part of a Postscript figure in a LaTeX document, using the graphicx package.
This is normally done using the bb= option in includegraphics, but doesn't seem to work in my implementation.
I simplified the tex file to its bare bones
\documentclass[12pt,preprint]{article}
\usepackage{graphicx}
\begin{document}
\begin{figure}
\includegraphics[bb=260 0 489 200,clip,width=\textwidth]
                      {4year_JMCv3_galnorm_lat.eps}
\end{figure}
\end{document}
I compile using XeLaTeX.
Instead of starting at 260 along X in the image the figure starts at 0, and keeps the first (489-260)=229 points of the image.
That is bb=x1 y1 x2 y2 always turns into bb=0 0 x2-x1 y2-y1
I gave the same file and image to a friend who has a different LaTeX package (on Mac) and it worked fine for him.
I must have something wrong in my installation, but I can't figure out what it is.
Did anybody see that behaviour?
Thanks for your help,
Jean

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