XVISTA can be run under MacOSX (10.3, 10.4, and 10.5 have been tested, and 10.6 to some extent), but several things are required to be installed:

X11 : available in Developers Tools (tested), also open source (xfree86)
gcc/g77 or gfortran : gcc available in Developers Tools, but g77/gfortran from open source
lynx : if you want help to work, open source
readline : if you want command line recall to work, open source