InstantSSL Certificate Installation: Microsoft IIS 4.x
Step 1. Install the Server file certificate using Key Manager
Go to Key Manager.
Install the new IIS SSL Server certificate by clicking on the key in the www directory (usually a broken key icon with a line through it), and select "Install Key Certificate".
Enter the Password.
When
    you are prompted for bindings, add the IP and Port Number. "Any
    assigned" is acceptable if you do not have any other IIS SSL
    certificates installed on the web server. 
    Note: Multiple
    certificates installed on the same web server will require a separate
    IP Address for each because SSL does not support host headers.
  
Go to the Computers menu and select the option "Commit Changes", or close Key Manager and select "Yes" when prompted to commit changes.
The new IIS SSL Server certificate is now successfully installed.
Back up the Key in Key Manager by clicking on Key menu> Export -> Backup File. Store the backup file on the hard drive AND off the server.
Step 2: Installing the Root & Intermediate Certificates:
Your
    IIS SSL Certificate will have been emailed to you. The email will
    also contain two other Certificates: the
ROOT certificate and
    Intermediate
CA certificate .Save
    these Certificates to the desktop of the web server machine.
    
    It
    is essential that you have installed these two Certificates on the
    machine running IIS 4. You may also download them from the support
    section of the website:
    
    Once you have installed the
    Certificates, restart the machine running IIS 4. You must now
    complete one of the following procedures - the procedure you follow
    is dependent on the Service Pack that has been implemented on your
    machine running IIS4.
Service Pack
    3:
    Install the
    above certificates in your Internet Explorer by opening each
    certificate and clicking "Install Certificate".
    
    Service Pack
      4: 
    Install
    the above certificates manually in a specific root store (you may
    also want to read (see Microsoft Knowledge Base Q194788):
- 
      Install the Root certificate by double clicking on the corresponding file this will start an installation wizard 
- 
      select Place all certificates in the following store and click browse 
- 
      select Show physical stores 
- 
      select Trusted Root Certification Authorities 
- 
      select Local Computer, click OK 
- 
      back in the wizard, click Next, click Finish 
Repeat the same for the Intermediate CA Certificate however choose to place the certificates in the Intermediate Certification Authorities store.
Service Pack
    5:
    Same as
    SP4.
Service Pack
    6:
    Same as
    SP5.
Reboot the web server to complete the installation.
 
                       
                       
                       
                       
                       
                       
                       
                       
                       
                       
                       
                       
                       
                      