Following are commands to be executed to install a template in MOSS Server. I have installed a site template for IT help desk with the following command. There are two steps to be basically.
1. Add solution:
C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN>stsadm -o addsolution -filename HelpDesk.wsp
Message shown execution is "Operation completed successfully."
2. Deploy solution:
While deploying we need to specify either the deployment is '-immediate' or '-local' or '-time' as parameter .
C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN>stsadm -o deploysolution -name HelpDesk.wsp -immediate -allowgacdeployment
Message shown execution is "Timer job successfully created."
Thats it :)