Hi.
OpenACS 5.7 Requires Postgresql 8.3 or higher.
I am upgraded two 5.2 sites recently to 5.7 with no problems.
Basically dump the database. Then import into Postgresql 8.3 database and then update your code to OpenACS 5.7 and start it up.
You should visit /acs-admin/apm/ and click "Install Packages".
I recommend a a three step upgrade.
1) upgrade acs-kernel, acs-authentication, restart
2) upgrade remaining core packages, restart
3) upgrade remaining optional packages, restart.
