Originally Posted by Net-Pet
It would be really nice if I can try it out and just change the ports from maybe 81 to 80 for the new installed apache, and change the other tcp ports to something that not conflict a active installation.
Don't change the port from 81 to 80. ISPConfig has it's own Apache (used solely for the ISPConfig web interface) that's running on port 81, whereas the normal Apache is running on port 80 (that's the one you administrate by using ISPConfig). If you change ISPConfig Apache's port from 81 to 80, it will interfere with your normal Apache so that one of them won't be able to start...