Well, I have installed CentOS 4.3 with the minimal package set and to make the ISPConfig self installer work you need to add some others RPM packages:
yum install mysql-server gcc flex mysql-devel byacc rpm-devel rpm-build
Another problem is the zlib package: the CentOS 4.3 version is “old” and some ISPConfig components refuse to compile correctly. I have crawled some FTP sites and I have got the zlib-1.2.3-1.2.1.src.rpm updated package from Fedora.
rpmbuild --rebuild zlib-1.2.3-1.2.1.src.rpm
rpm -Uhv /usr/src/redhat/RPMS/i386/zlib-*1.2.3-1.2.1.i386.rpm
After these simple steps, the ISPConfig auto-configure script will run nicely 🙂