Unless some of the things you wish to run require a specific version of postgres, I would suggest that you go with the most recent, current version, which is postgres8.3. As well as continuing performance improvements, Later versions have very useful features.
For instance, 8.2 added the INSERT INTO ... RETURNING feature, which very neatly solves the problem of recovering the automatically generated id of a just-inserted row -
Code:
INSERT INTO table (text, number, date) VALUES ('Hello World', 42, '2008-06-05') RETURNING id;
I don't know what goodies are available in 8.3, but check out
the release notes at postgresql.org should tell you. It seems like updatable cursors are the big addition.