After the latest upgrade in debial lenny with apt-get upgrade, it reports version number 5.0.3, so the latest ispconfig_install stops with an error "Your operating system is not supported". I could trick the install by changing the /etc/debian_version but should I wait for another Ispconfig 2 release that will support the latest debian lenny?
I recommend that you change the /etc/debian_version file to 5.0, install ispconfig and then change the file content back.