>
...
> But, is it possible anyway to say \usepackage
> {utopia} or \usepackage{fourier} in a XeLaTeX file ?
>
I think it is possible. If you are on Mac OS X,
try to use the driver xdvipdfmx by
xelatex --output-driver='xdvipdfmx -q -E' foo
Best,
Akira