[XeTeX] Getting LaTeX math font packages to work?

[J. P. Blevins]

Until TFM files for OpenType math fonts are available, I've been trying to 
get standard LaTeX math packages to work with XeTeX, with rather mixed 
success.

If I load the mathtime package: 

\usepackage{mathtime} 

BEFORE I declare OpenType text fonts:

\DeclareFontFamily{U}{AdobeGaramondPro}{}
\DeclareFontShape{U}{AdobeGaramondPro}{m}{n}%
     {<-> "Adobe\space Garamond\space Pro:+onum"}{}
...

then I get the following error:

kpathsea: Running mktextfm Adobe 
/usr/local/teTeX/share/texmf/web2c/mktexnam: Could not map source 
abbreviation A for Adobe. /usr/local/teTeX/share/texmf/web2c/mktexnam: Need 
to update /usr/local/teTeX/share/texmf.tetex/fontname/special.map? 
mktextfm: Running mf-nowin -progname=mf \mode:=ljfour; mag:=1; nonstopmode; 
input Adobe This is METAFONT, Version 2.71828 (Web2C 7.5.2) 
(/usr/local/teTeX/share/texmf.tetex/web2c/cp8bit.tcx) kpathsea: Running 
mktexmf Adobe

! I can't find file `Adobe'.
<*> ...e:=ljfour; mag:=1; nonstopmode; input Adobe
                                                  
Please type another input file name
! Emergency stop.
<*> ...e:=ljfour; mag:=1; nonstopmode; input Adobe
                                                  
Transcript written on mfput.log. mktextfm: `mf-nowin -progname=mf 
\mode:=ljfour; mag:=1; nonstopmode; input Adobe' failed. kpathsea: 
Appending font creation commands to missfont.log.

! Font \U/AdobeGaramondPro/bx/n/14.4=Adobe not loadable: Metric (TFM) file 
or A TSUI font not found. <to be read again>
                   G
l.98 \section{Introduction}
                           \label{intro}
? 


If I load the mathtime package AFTER the OpenType font declarations, I 
avoid the error. HOWEVER, all of the mathtime glyphs are offset in the 
resulting PDF. Omegas show up in place of thetas, left angled brackes are 
replaced by right angled brackets, etc. (The mathpi package exhibits a 
similar offset with mathbb, mathscr and mathfrak fonts.)

The mathtime fonts are active in Mac OS (and the corresponding .pfb fonts 
are in the appropriate font directory in the TDS), and are listed in 
psfonts.map.

Any suggestions would be welcome; I am also prepared to use the Lucida New 
Math fonts, if someone has managed to get them to work with XeTeX.

Thanks,

-Jim