I have exactly the same issue, but php-mysql is installed.
I have followed this guide:
closely and worked through various errors as they have arisen. I am at the final stage (of course)
7.2) Installation from SVN
yum install subversion
svn export svn://svn.ispconfig.org/ispconfig3/trunk/
7.1+7.2) Now proceed with the ISPConfig installation.
Now start the installation process by executing:
php -q install.php
and when I type in that final line, ISPConfig starts up. It asks 3 questions, language, installation mode and FQDN, but when I answer the last question, I get:
No PHP mysql functions available. Please ensure that the PHP mysql module is loaded.
Every test I run indicated that php5-mysql is, in fact, installed and running so I am now lost and this thread is the only hit I get when I google the error.
Any tips would be most gratefully received.
I am actually running CentOS 5.4, but I hope the setup is the same as for 5.2 - it's the closest thing I could find.