If you already have your SSL Certificate and just need to install it, see
SSL Certificate Installation :: iPlanet.
How to generate a CSR in Netscape iPlanet Web Server
In a browser window, log in to the web server and choose the server you are securing.
On the Security tab choose Request a Certificate.
Fill in the required information. When you click OK, the CSR for your SSL Certificate will be emailed to the address you specify.
Copy and paste the CSR (including the BEGIN and END tags) into the DigiCert order form.
After you receive your SSL Certificate from DigiCert, you can install it.