To install the argon.org CA certificate select this link and follow the prompts your browser gives you. If it asks you whether to open or save the file, choose "open". If this doesn't work with your browser (it only lets you save the file, or opening it displays it on the screen instead of opening a special window), there are some good browser-specific notes at the Rutgers RULink project. If you have any questions please contact email@example.com.
Here's the certificate revocation list (CRL).
For most people, the prefered way to access the certificate is via the link above. Here are the certificate in PEM format and CRL in PEM format for when they're useful.