To view the PostScript documents, you should get ghostview/ghostscript. The home page for Ghostscript and Ghostview is at http://www.cs.wisc.edu/~ghost. The FTP site is ftp://ftp.cs.wisc.edu/. Mac, UNIX and PC version of Ghostscript are available there.
In order to view PDF files, you will need a copy of Adobe's free Acrobat Reader.
Files with the .gz extension will need to be uncompressed using a gzip program. See http://www.gzip.org/ for more information.
Linux/UNIX: For information about gzip, see the GNU web page on How to get GNU Software at http://www.gnu.ai.mit.edu/software/software.html.
Macintosh: Several disk utilities are available that support GZIP.