Marcos Antonio,
In addition to the link Jade gave you from the FAQ[1], this older information may have some value to you:
http://web.archive.org/web/20020906081532/https://openacs.org/doc/openacs/html/oracle-to-pg-porting.html
A newer version of this document may still exist on openacs.org, but I could not find it.
best wishes
Torben
1. https://openacs.org/forums/message-view?message_id=147663