[XeTeX] Ancient Greek hyphenation

[Manny Ram.]

Hello, I'm a new Xetex user, and am having troubles
with Ancient Greek hyphenation. I searched your
mailing lists' archive for answers, but they seem
unintelligible to  me. Would any of you be willing to
help? Mind you, that I'm a novice still, and know very
little about Tex, so please try to keep the answer as
simple as possible.

The code used in TexShop:

%!TEX TS-program =  xelatex
%!TEX encoding =  UTF-8 Unicode

\documentclass[BCOR12mm,DIVcalc]{scrbook}

\usepackage{fontspec,xltxtra,xunicode} % I inserted
this because it works, but I don't know exactly what
it does
\defaultfontfeatures{Mapping=tex-text} 
\setromanfont[Mapping=tex-text]{Hoefler Text}
\setsansfont[Scale=MatchLowercase,Mapping=tex-text]{Gill
Sans}
\setmonofont[Scale=MatchLowercase]{Andale Mono}

\newfontfamily{\G}{Galatia SIL}

\begin{document}
	
{\G 
Ancient Greek Text
}

\end{document}

Up to here, I managed to display Greek fonts
correctly, but I get overfull boxes and don't see any
hyphenation. 

Then I downloaded a Greek hyphenation package
specifically for Xetex containing the files
xgrahyph.tex, xgrcodes.tex and xgrmhyph.tex, and put
the folder in my version of the Tex directory at
usr/library/texmf/tex/latex (btw, I'm using Mac OS X.)
After that, I changed the language.dat file by
disabling greek (which I assume is the non-unicode
version) with the % sign, and added another "greek"
with xgrahyph.tex. Finally, I ran fmtutil --all.
Nothing.

What am I doing wrong?

Thanks,
Augustinus

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