This problem occurs when you uninstall MS Office Communicator 2005 (MOC 2005) and tries to reinstall it. It will generate an error message "This installation was interrupted. No changes were made to your computer system. Please try running the installation again."
This is because security hotfix KB974571 prevents the reinstallation of MOC 2005.
Follow these step to reinstall MOC 2005
1. Start -> Control Panel -> Add or Remove Program
2. Tick show updates to display security updates
3. Look for KB974571 and remove it
4. Restart your PC
5. After restart, you should be able to install MOC 2005.
6. As a security measure, you should reinstall KB974571 (download here) after successful installation of MOC 2005
This was taken after reading a long post and feel that summarizing the solution will help others.