By default, PS file is printed in Portrait orientation. It can be simply rotated to Landscape or Rotated Landscape (180 degree oppsite of Landscape orientation) by adding "%%Orientation:" directive:"

%!PS-Adobe-3.0
%%Pages: (atend)
+%%Orientation: Landscape
%%BoundingBox: 14 9 495 650
%%HiResBoundingBox: 14.900000 9.900000 495.000000 650.000000
%.......................................
%%Creator: GPL Ghostscript 871 (pswrite)
%%CreationDate: 2012/02/02 17:38:24
%%DocumentData: Clean7Bit
%%LanguageLevel: 2
%%EndComments
Remember to remove "+" from the very begining of line 3.
PS: setting orientation for printer under Windows O.S.:

XP: from device and printers menu, right click on printer icon, then properties, going to advanced tag, then press "Printing Default" button to change orientation.

Win7: from device and printers menu, left click on printer icon, then click on "Printer" on top left to find properties, and rests are the same as XP.