The problem is in fedora 11 and not in ISPConfig. ISPConfig itself works perfectly on any fedora version, but as long as system requirements like courier /which is a very widely used imap server) can not be compiled on fedora 11, you can not install ISPConfig.
Fedora 11 is not a good choice for a server as it tends to break setups from time to time as they try to use only bleeding edge software which is a bad strategy for a server. To run a server, better use e.g. centos which is a clone of rhel and which is made to run servers.