I know ISPConfig is intended to run on a new server with no sites. If I was to install it on an existing server, would it disable the existing sites? If ISPConfig alters the current httpd.conf, then I guess the anwser would be yes. Thanks.
It doesn't really disable them, but things such as PHP and Perl won't work anymore because ISPConfig disables them globally and enables them on a per-site basis.