OID for pg_get_functiondef

I've just started working on an 8.4 database and I have been asked to
extract all the functions source code stored in various databases and
schemas so they  can be put into a repository for the developers.  I'm
planning to use  pg_get_functiondef(OID) but I am having a hard time
finding the OID for functions.  I've looked into the
information_schema and the pg_catalog schemas and have found
information on functions but none of them seem to have the OID of the
function.  Can anyone please tell how to get the OID for a function
within a schema  and or if there is a better way.

Thanks