Astrometry is written for UNIX-like systems (like Linux), but Mac OS X is one of those too...check out the Astrometry build instructions...
http://astrometry.net/doc/build.html#build
If you have any experience with compiling software in a Linux environment it should be pretty straightforward.
Incidentally, the Windows build of astrotortilla bundles Cygwin, which is a UNIX-like environment that runs on top of Windows.