1. Make backups!!
2. Upgrade OS first, then ispcp
3. Be *extremely* careful when asked about what to do with new default configuration files (you should manually inspect the differences and add whatever new directives make sense instead of replacing old files with newer directly).
4. Don't forget this step from the update process (after having updated your system to lenny):
Code:
# aptitude update && aptitude safe-upgrade
# aptitude install lsb-release
# aptitude install $(cat ./docs/Debian/debian-packages-`lsb_release -cs`)
This will take care of any missing packages you may have after updating.
5. During the whole upgrade process your services will be down. I recently updated a heavily loaded system (+200 accounts, +1500 mailboxes) from etch/1.0.0 to lenny/1.0.6 and it took me near 4 hours. Assume that it will take some long time, warn your customers about the outage and stay calm, because trying to rush it will probably destroy your system.
Good luck!