[XeTeX] problems helping a new Mac user

[François Charette]

Apologies in advance if this is not totally XeTeX-specific. But there 
are so many MacTeX users on this list that the temptation to be lazy is 
great...

As a linux user who is not totally familiar with MacOSX, I am trying to 
help a colleague who wants to use XeTeX to typeset Arabic on his new 
MacBook with my arabxetex package. He is pretty new to TeX (but being in 
a maths department, he has some basic concepts). I gave him instructions 
on how to install MacTeX, which he did. He then installed arabxetex 
under ~/Library/texmf/ and ran “texconfig rehash" in the terminal. 
xelatex seems to work well, except that arabxetex.sty could not be 
found. I figured out that the paths in his HOME directory are not 
included in the $TEXMFDBS variable, so that mktexlsr ignores it 
completely. I told him to make appropriate changes in texmf.cnf, 
thinking that on a Mac it would be under
/usr/local/texlive/2007/texmf/web2c/,
but he tells me that /usr/local is empty, which of course cannot be.

Can someone tell me I could explain a beginner how to edit his texmf.cnf 
file ?
Perhaps "sudo <Some_Editor> /usr/local/texlive/2007/texmf/web2c/texmf.cnf" ?

And why is it that on a default install of MacTeX TEXMFHOME does not 
seem to be part of TEXMFDBS ?

Thanks in advance,
François