Well, on Mac OS X the Preview application uses the utility pstopdf to
convert PostScript files to PDF and displays the latter.
The default page size pstopdf uses seems to be US Letter in portrait
orientation.
You should modify your PostScript setup to generate a correct
setpagedevice statement for e.g. A4 landscape format to ensure that the
resulting PDF is correct.
By the way, the gv utility (not standard on Mac OS X but on Linux) dieplays
the file correctly.
Helge