protopg (formerly known as oratopg) tries to implemente a parser that on the fly translates SQL and PL dialects from Oracle's variant to the standard and/or PG variant. It's in an proof-of-concept/alpha stage. It hopefully will appear on pgfoundry soon.
ora2pg is (as far as I know, but it's a long time since I used it) a Perl tool that can read data from oracle DBs and store into PG DBs. Think of an export/import tool. It's considered stable. It's part of PostgreSQL's contrib package.