no builds here http://code.activestate.com/ppm/Math-PARI/

no apparent 64-bit builds here :( ppm install http://www.bribes.org/perl/ppm/Math-Pari.ppd

or here http://strawberryperl.com/release-notes/5.18.0.1-64bit.html

Could try self-build of http://strawberryperl.com/package/kmx/perl-modules-patched/Math-Pari-2.01080603_patched.tar.gz after installing patch/gcc 4.6.x from http://sourceforge.net/projects/perlmingw/files/

This might be workable, might need other patches, How to install CPAN modules into ActivePerl

OTOH, http://strawberryperl.com/release-notes/5.18.0.1-32bit.html comes with pari, and will run on a 64-bit windows (like all 32bit programs)