This is a modified PPD file that gives 600dpi on an NEC SuperScript 870.  
The printer can do the resolution just fine, but the default driver only lets 
you select 300dpi.  This has been known since early 2004, and it's late 2005, 
so I figured I'd toss this out for anybody looking for something like this.

Reference:
  http://www.linuxprinting.org/pipermail/nec-list/2004q1/000034.html
  
--
Evan "JabberWokky" E.