Originally Posted by falko
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...
If you have 2 ip addresses you can set them up to run on a seperate ip address without any problems.
I have done this and have ISPConfig on port 443 on 1 ip and apache running on another ip on 80 & 443. So far it seems to be working great.