To get Netscape to automatically open a postscript file with Ghostview, do the following:

In Netscape, go to menu item "Edit: Preferences", the open "Navigator" and go to "Applications".  Create
a Postscript MIME type by click "New" and enter the following information:

Description: Postscript Document
MIME Type: application/postscript
Suffixes: ai, eps, ps, epsf, epsi

Click "Application" button, and type:

ghostview %s

in box.

Click "okay".