There is a ghostscript driver called hp850 which you can
find at http://www.erdw.ethz.ch/~bonk/hp850/hp850.html.
Version 1.3 of this driver works very well and drops
seamlessly into gs 5.10 which is the version included with
RedHat 6.0.  I have been using it in RedHat's environment
simply by replacing the default gs with my own that includes
this driver, and then editing postscript.cfg to change the
name of the driver to use and the resolution.

This driver is included by default in all versions of
ghostscript > 5.50, so if you take no action on this, you'll
get it by default in a year when those versions of gs
default to the GPL. In the mean time, it would be a nice
addition as it will allow those of us with HP deskjet 850,
870, 890, and a few other printers to print from RedHat
without having to make special modifications....