Add mcrypt to ispconfig php
I was able to add mcrypt without recompiling.
My /etc/php.ini used "/usr/lib/php/modules" for its extension_dir. So I used it in the ispconfig dir. Your modules dir maybe different depending on your distro.
edit php.ini in /root/ispconfig/php
extension_dir = "/usr/lib/php/modules"
I have ispconfig 2.2.24 with Fedora9
You could also create a dir in /root/ispconfig/php
cp /usr/lib/php/modules/mcrypt.so /root/ispconfig/php/modules/mcrypt.so
extension_dir = "/root/ispconfig/php/modules"
Recompiling may depend on you distro as well.