Please help for a beginner

Dear all,
I have just come to OJB, and it was my intention to use ODMG.
Is there any tutorial?

I would like to retrieve a collection of objects from a relational
database (Postgres), making a selection using non standard database
functions (postgis extension).
I was wondering:
1) if this is possible with ODMG?
2) if the above is possible, then what is the configuration I should make
up, and what the query should look like?

Thank you,
Francesco.