Caution: Flying pans at low altitude.
Get a mac build of ONScripter and copy nscript.dat, arc.sar, arc.nsa and default.ttf from a Windows installation of Tsukihime English. You can get the latest ONS builds here. I did a quick test on the win32 build of onscripter-en-20090902 and it appears to be working. If you have any problems you can either post here or in this thread in gemot.