PostScript is a trademark of Adobe Systems Incorporated.
Neither of these programs are in any way connected to Numerical Recipes Software. We know that they can be tricky to install and get running, but (sorry) we cannot provide any assistance in doing so. There are active user groups on the net that can often be helpful, e.g., gnu.ghostscript.bug and comp.lang.postscript.
The first place to look for information on Ghostscript and Ghostview is the Ghostscript Home Page. Presumably, this information will be kept current by its maintainers (not us!). There is also a semi-commercial (though unsupported) version, with better fonts, available by mail at a reasonable price from Aladdin Enterprises.
Here are a few, some older, downloading points known to us at the time of writing. You want to get both Ghostscript (often named "gs261..." or similar) and Ghostview (often named "gsview..." or similar) for full effectiveness: