Here are some programs that will work: gunzip (Unix, Windows, and Mac), Win Zip (Windows), Stuff It Expander (Macintosh, Windows).
Depending on your browser, you may be able to install a plugin that allows you to view the files directly in the browser.
Alternately, you can save the file to disk, and view using the Acrobat reader as a standalone application.
If you have a postscript printer, you can print the files directly.
Otherwise, you can print from the ghostscript-related programs described above (Windows and Mac) or use the (sometimes hard to find) Drop*PS utility (Mac), all of which can print to non-postscript printers as well.
Portable document format (pdf) files are viewed with the Acrobat reader, which can be downloaded from Adobe's web site.