Before requesting or renewing a Live Communications Server (LCS) 2005 certificate, you need to install the LCS Resource Kit (download).

In the resource kit is a tool called : LCSCertUtil.exe

LCS Cert Utility
The LCS Cert Utility tool generates certificate online and offline certificate requests and import a certificate response issued by an offline CA (certification authority). It also allows users to delete certificates from the partner certificate store in Access Proxies.

When you want to request or renew a certificate, start the LCS Certificate utility.

Request LCS Certificate

Make LCS Certificate Request

You need to fill in a CA. If it’s a CA that is not available, then the tool will notify you and save the request file in a .req file.
If you use the template (in this case LCS2005Computer), you need to make sure that the template is also on your CA.

After clicking Next you’ll receive a messsage the text file is created. With this request file you can obtain the certificate. After the certificate is obtained start the LCSCertUtility again and select import.
The Certificate will be added to the local certificate store of the computer. The certificate also has the private key, which is needed for the LCS Server.

Now you can add the new certificate to LCS through the management interface. After you placed the certificate and LCS is not starting correctly and you receive event id 14397, follow the article I placed regarding this issue.